I hate to generalize, but never in my experience (I am over 40) have I ever even seen a resume with potential ever get turned away due to age.
No one has ever told me they turned someone down due to age, but probably because it is against the law.
We interviewed a guy who knew what we were doing inside and out, and he was older than all of us. On top of this, he had a nice, friendly personality. We had been interviewing for this position for a while. The lead and manager turned him down. He would be paid less than a Google L3 would get paid (this was ten years ago, and it was not a tech company). I protested saying "what are you looking for? If he isn't good enough, what are you expecting to come in? what was wrong with him?" The reply was "I don't think he would be happy if we called him at 3 AM if some problem came up". The problem was they thought he was too old. He was probably in his late 50s.
If the manager are actually attempting to do this pathological move, a staff or PE will notice and work to correct that issue with senior management. Otherwise engineers leave as it removes their growth areas.
At least at non-pathological places.
...And who would?
But is she a cultural fit? Does he have the energy? A bit too senior?
I imagine it plays out like that too much the same effect.
I was a recruiter for 9 years. Discrimination at an individual level is rampant, but the type of discrimination varies.
One hiring manager told me a woman was the best he’d interviewed, but he heard kids in the background & wouldn’t hire her because he didn’t want to risk her going out on maternity leave.
A manager told me he threw out all resumes with names sounding like they’d be from a specific country because he thought they all had poor communication skills.
It’s really common for hiring managers to insist on 3 to 5 years of experience because they’re likely to be young and willing to work a lot of unpaid overtime.
They wouldn't throw it away publicly in a meeting since it's illegal, but when a recruiter is browsing LinkedIn profiles trying to find potential candidates to interview, I'm pretty sure they dismiss older candidates as they don't perform as well in the coding interviews.
That being said, I know FAANG make a big deal of trying to interview as many minority candidates as possible and incentives recruiters to do so but AFAIU older candidates don't fall in the "minority" category.