People don't look at a surgeon aged 55 asking themselves why that surgeon failed to move on to the next level. Unfortunately the same isn't true at all for programmers, for some reason it's assumed to be an entry position. If the path to surgery would be through nursing experience, aging nurses would have a much lower standing amongst all their future surgeon peers than they have now.

Seen from this angle, the ageism seems to be an unsurprising outcome of the relatively informal qualification structure in software tech: apparently opportunity for all cannot come without a bit of stigmatization for those who refuse to strive for it.