In fairness/completeness, here's a very-formal biographical note that combines retirement and 卒業, moving on from a lifetime of work at Honda before going on to different things.
2011年に⾃動⾞技術会フェローに認定。2012年グローバルテレマティクス部部⻑兼役員待遇参事に就任し、テレマティクスサービスのグローバル展開を担当し、2015年定年退職でHondaを卒業。
http://guide.jsae.or.jp/event/215215/

女子アイドル転換期　グループの顔が卒業する理由
https://style.nikkei.com/article/DGXMZO37847820W8A111C1000000/
Tables, charts, statistics, elaborate discussions on why various band's head performers eventually "graduated".

term-of-art:
See https://ja.wikipedia.org/wiki/AKB48
Search 卒業予定 
This reflects how the term is used in the industry.  Talents "graduate".  I probably should not have called this euphemistic anymore.
If you search 卒業 alone in the article you'll see how tied up this is in the industry.
Japanese Wikipedia has hundreds of articles on bands and performers using this terminology.

English:
SOTSUGYŌ: TOO OLD TO BE AN IDOL?
https://the-comm.online/blog/sotsugyо-too-old-to-be-an-idol/

退職	5926900
会社を退職	80060

会社を卒業	3597
vs 

卒業公演	24421            Graduation performance/concert held before members depart, (granted, some overlap with school graduation events)
卒業コンサート	6935.    
卒業メンバー	4901	 Graduated group members
グループを卒業	1484.    Left the group
卒業を発表	1255	 Someone announced they would be "graduating" (one formulation) 
卒業シングル	239 Single (music track) released along with a band member's graduation

Note: The n-gram database doesn't contain numbers or romaji, and most band names do. Something like "AKB48を卒業した" would likely have generated quite a number of hits.

something else to chew on.  
Surely this is vt.  会社を卒業した。
sankoku says 名・他サ.  I graduated [college]...

大学を卒業して	95169	99.9%
大学から卒業して	127	0.1%

=== 

I wrote up quite a few additional comments on this, but I don't want to speak entirely based on my ability to google things, and limited personal exposure to these terms.  

This is an entry of some personal interest to me, not just something I pulled out of a hat and googled. I'd appreciate if you leave this open for a few days, if it's not in anyone's way, and I will chat with some natives here about their opinions. Or if it's alright for me to re-open later, that would be fine too if you want to discard changes for now. 

I had tightened the gloss a bit, so I'll leave that for reference. I've also changed[2] to be more specific about where you are moving on from, which I think helps capture "departure from a company", and mirrors the daijs defn(ある段階や時期を通り過ぎること). I've also left some refs on this as a "term-of-art" if anyone wants to chew on it(calling this a "euphemism" bas a poor choice on my part).  A key point in my mind is that, as a well-defined, well-known, established term-of-art, 卒業 merits a gloss of "retirement".  But I don't think "retirement" belongs in sense[2], and really should be limited to the idol case.  "graduation", in this sense of "retirement", would carry an identical, specific meaning, even if there is some sense-overlap with Hondaを卒業.   

hmm... Honda was specifically 年定年退職でHondaを卒業, so retirement is covered by 退職, and 卒業 is "moving on from his time at", so I'm not sure this is really counter to my intuition here... 

With regards to the two new linked refs - the twitter link was to a young, female actress/theatre performer, so her use does not seem so surprising.  For the "style" article, I think you're correct that this is sense[2].  It definitely appears that sense[2] is being used euphemistically now as a preferable term for leaving a company.  But I don't think this use post-dates, and also does not adequately cover, the JPOP/idol case.  I'll ask around for more Japanese opinions...

Anyway, I always appreciate everyone's consideration

@@ -19 +19 @@
-<pos>&vi;</pos>
+<pos>&vt;</pos>
@@ -26,2 +26,2 @@
-<pos>&vi;</pos>
-<gloss>moving on (from)</gloss>
+<pos>&vt;</pos>
+<gloss>moving on (from a stage of one's life)</gloss>
@@ -33 +33 @@
-<pos>&vi;</pos>
+<pos>&vt;</pos>
@@ -37 +37 @@
-<gloss>graduation (used euphemistically, indicates departure from a talent agency or performance group, usu. on good terms)</gloss>
+<gloss>graduation (pre-announced departure from a talent agency or performance group, usu. at a young age)</gloss>

I think this is just a case of sense 2 being used. I don't think it needs its own.

https://style.nikkei.com/article/DGXMZO27540540R00C18A3000000?channel=DF130420167231&page=3
会社を退職ではなく、「卒業」する人が増えるわけ
...
そして、その結果、「会社を辞める際に、人生の次のステージに進むことをイメージさせる卒業という前向きな言葉で、退職を表現するようになっているのではないか」と推測する。

https://mobile.twitter.com/asumi_momokawa/status/1550490187662528512
営業時代の同期が会社を卒業したらしい。

I don't agree with this edit.

メンバー加入・卒業・脱退・解雇　: Graduated, departed, or terminated...
https://idol-report.com/category/member

乃木坂46斉藤優里が卒業発表 (Marcus's original reference for "leaving a group, company"/"quitting" sense)
In which 25 year old woman announces "retirement" from female idol/pop performance group "Nogizaka46"
https://www.nikkansports.com/entertainment/news/201903250001019.html

https://nichegamer.com/amano-pikamee-announces-graduation-at-the-end-of-march/
Note the quotation marks:
Pikamee has announced that she will be “graduating” at the end of March
For the uninitiated, a VTuber “graduation” effectively means a retirement of the actress (or at least character!) from the industry. The term is borrowed from idol culture which usually says their talents graduate when leaving the group.

Performer announces their own 卒業, english translation is "retirement":
https://twitter.com/ayaki_piano/status/1440312921033089037
TRIX卒業の件では申し訳ありません。ファンの皆様へメッセージを書かせて頂きましたので、御一読頂けましたら幸いです。
I'm sorry about my retirement.I wrote my message to all of our fans, so I would appreciate if you could read it.Thank you.

https://en.wikipedia.org/wiki/Japanese_idol
Retirement
Idols are typically expected to change careers after aging out of the industry, with female idols ... at age 25[37] and male idols at ages 30–45. The term originated from the idol group Onyanko Club... Prior to the 1980s, the terms "retirement" and "disbandment" were used.[40] ... Tsunku, who produced the group Morning Musume, used the term as a euphemism regarding one of the members leaving the group.[40] An idol having a "graduation" ceremony is seen more favorably than terminating a contract or voluntarily withdrawing, as the latter two terms are negatively connoted with scandals.[41]

アイドルの動画を見ていて思いました。大人はその後の生活の責任など取らないのですね。
https://eikaiwa.dmm.com/uknow/questions/84410/
また、「卒業」のニュアンスは、「次のキャリアに行く」と言う意味ですよね。
ならば、これは日本的な考え方で、「Graduation」じゃなくて「Retirement」の方が良いです。
したがって、調整したら「Their lives after retirement from showbusiness were miserable」になります。「Showbusiness」はエンタメ産業のことです。

Idol singer from Keyakizaka46 says she’s now working as a Tokyo bar hostess
https://japantoday.com/category/entertainment/idol-singer-from-keyakizaka46-says-she’s-now-working-as-a-tokyo-bar-hostess-1
Youth is highly prized in Japanese show business, doubly so in the music sector, and triply so for idol singers. That means many idols retire from performing, or “graduate,” to use the industry term, at an age when they’re far too young to retire from working entirely.

All Hololive Vtubers who ended their activities
https://vocesabianime.com/eng/all-hololive-vtubers-who-ended-their-activities/
1 - Hitomi Chris: Termination Date: June 25, 2018
Hitomi Chris, who had her contract terminated by Hololive after some internal bullshit....
2 – Yakushiji Suzaku Graduation Date: March 6, 2020
...
7 – Kiryu Coco Graduation Date: July 1, 2021
8 – Uruha Rushia Termination Date: February 24, 2022

If you want a sense of just how common suggested sense [3] is, google news: 卒業 AKB48
For English, google unquoted: graduation retirement idol

The "retirement" sense of 卒業 has a well-documented history(tied to a specific band/performer's departure), and a very specific use case (you wouldn't 卒業 from your career at Sony). It is for Japanese "idols" or other (generally young) performing talent who retire (or frequently "are retired") from their agencies, often for aging out.  For women, this is at ~25, for men ~35. But it can be applied any time a talent agency and their respective talent part ways for any reason.  It is, among other things, a way of saving face for both parties. (preferable to "fired", "terminated", "dismissed", etc.)

In Japanese, a previous common term was 脱退, which appears in the Japanese Idol wikipedia page talking about departures: "メンバーの脱退や卒業..."

The citation used when Marcus added "leaving a group, company" was an example of precisely this sense (see refs). A 25 year old idol retiring from the female pop group "Nogizaka46". 

卒業 grew as euphemism for 脱退 in Japanese.  Because "graduation" does not (or did not previously) exist euphemistically in English, this has often been translated as "retirement" for comprehensibility. As Japanese pop culture makes inroads in the west, the term "graduation" is more-and-more used directly (both because it is now understood, and also because "retirement" is a very harsh term that some performers don't want to use).

Terms like "graduating" and "graduated" in this context are often used in quotes, not only because they might not be understood, but specifically because they *are* understood to be euphemisms.

This term remains in active, common use in English, now used with "VTubers" (live-streaming talent on youtube or other services), as well as the established J-POP scene.

I added "on good terms"... I've seen this detail many places, but perhaps it's not critical.  See the last reference - if a talent is terminated for cause, it becomes a shameful affair. Their existence (music, biographies, etc.) is often wiped from any platform the agency manages, and are somewhat left to disappear.  "graduation" as a preferable euphemism applies when parties split on "amicable" terms. (performers generally announce they they have "decided on their own" that it is time to graduate, whether this is this case or not).

I'm sure I haven't done the [note] properly, I appreciate any help in organizing this.  For this sense, "retirement" and "graduation" are absolute synonyms, but I didn't want to repeat the explanatory bit.

@@ -29,2 +29,10 @@
-<gloss>leaving (a group, company, etc.)</gloss>
-<gloss>quitting</gloss>
+</sense>
+<sense>
+<pos>&n;</pos>
+<pos>&vs;</pos>
+<pos>&vi;</pos>
+<xref type="see" seq="1014340">アイドル・1</xref>
+<xref type="see" seq="1416570">脱退・だったい</xref>
+<s_inf>this sense is generally limited to Japanese idols and similar managed talent</s_inf>
+<gloss>graduation (used euphemistically, indicates departure from a talent agency or performance group, usu. on good terms)</gloss>
+<gloss>retirement</gloss>

@@ -18,0 +19 @@
+<pos>&vi;</pos>
@@ -24,0 +26 @@
+<pos>&vi;</pos>

@@ -20 +20 @@
-<gloss>completion (e.g. of a course)</gloss>
+<gloss>completion (of a course)</gloss>
@@ -26 +26 @@
-<gloss>outgrowing something</gloss>
+<gloss>outgrowing (something)</gloss>

Both GG5 and 中辞典 have "outgrowing".

A:「よっ！またユーフォー探しか？」
B:「俺たちもう５年生なんだぜ！そろそろユーフォーとか卒業しろよ！ 」
C:「なんで？ユーフォーは本当にいるのに」

@@ -25,0 +26 @@
+<gloss>outgrowing something</gloss>

"乃木坂46斉藤優里が卒業発表「全て出し切った」"
https://news.yahoo.co.jp/pickup/6318299

@@ -25 +24,0 @@
-<gloss>outgrowing something</gloss>
@@ -26,0 +26,2 @@
+<gloss>leaving (a group, company, etc.)</gloss>
+<gloss>quitting</gloss>

Neither sense is [adj-no].
I don't think [col] is necessary for sense 2.

@@ -19 +18,0 @@
-<pos>&adj-no;</pos>
@@ -26,2 +24,0 @@
-<pos>&adj-no;</pos>
-<misc>&col;</misc>
@@ -29 +26 @@
-<gloss>moving on</gloss>
+<gloss>moving on (from)</gloss>