throwawayforme
Internally, I believe we were told that all SWEs were expected to be capable of growing into a level 5 (senior SWE) role, and it was "OK" to not be promoted any higher.
So if somebody was hired in their 20s, it would be reasonable to expect they'd plateau at level 5 by 40, and would have shown most of their growth in their late 20s and early 30s. Would you hire this same person?
This was MTV, and it was several years ago, so perhaps things have changed.
I admittedly know very little about the hiring process. The whole hiring, interview process at Google just pissed me off in general so much that I refused to participate when I was there -- never even took the interview training.
When we interviewed for our jobs, we were lied to and told we were not doing technical interviews (which it turns out is Google company policy for handling acquisitions, according to a friend of mine from school who was a CTO at a different acquired company). So there I was, at 40ish, totally cold, being asked tech interview questions drawing on uni stuff I hadn't seen in 20ish years. I flubbed the interview, and came in one level below my peers. (though I was promoted after 2 years to the level I was working at). I almost refused to go for the promo, but just treated the entire thing as a joke and wound up getting it easily.
I think this happened to my wife, but her job category was not listed. When my small company was acquired by Google (and I had to interview to keep my job), we were forced to re-locate across the country from the east coast to Mountain View. My wife is a stats professor with tenure at a mid-tier university on the east coast, and she moved with our family. As its hard to get a tenured academic job, we found something at Google that sounded exciting to her.
She applied to Google for a Sr. Data Scientist job, and passed the phone and on-site interviews with flying colors. However, she was rejected by the committee. The problem was that, at Google, the committee both decides if you passed your interview, and then decides on your job level. The job level is arrived at using past work experience.
In my wife's case, the problem was that the committee deadlocked on how to level her. She had 5+ years of academic experience, and 5+ years of research experience (think national lab type stuff; research w/o teaching). However, she'd only briefly worked in industry many years ago between her MS and PhD. So rather than hire her, they told her to "go work someplace else for a year, then apply again". (direct quote, as relayed by her recruiter to me, as I referred her)
If she was a fresh PhD, there would have been no problem. She would have been hired as a level 4, and everything would be fine. But given that they didn't know how to rate her experience, it was just easier for them to pass on her entirely. This tends to bias the hiring process to hiring younger folks, without experience.
And, BTW, that's why I'm no longer at Google, and we're all back on the east coast.