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.