None of this addresses the real reasons why it's hard to get hired after 50 (actually, it starts in the mid-30s). It's not that older people are always at technology (they aren't) or that young workers don't want them around (they do). It's that bosses assume that anyone who isn't one of them by a certain age is either embittered or was anti-authoritarian from the start. Which isn't false.

To be honest, the old people who are obviously fading might be an easier sell to bosses than the ones who are 50, 60, 70+ and still rock solid, because with them, you really have to wonder what went wrong that they're still in the running for subordinate positions. (I mean, there could be—often are—a million reasons why an excellent person's career might go sideways, but bosses aren't usually the forgiving type. They still want to believe the system works, because they are the system.)

Bosses want to feel young again, but they also know that workplace subordination is humiliating and that older people are likely to have figured this fact out, while young people still think they're going to be invited to join the execs within 3 years (which the vast majority of them won't).