GP and GGP are not saying there is an overt conspiracy especially among interviewers; they are attempting to point out that the interview process itself is discriminating.

I'm sure the people that perform interviews are not discriminating and I'm certain a number of bright, older, time-squeezed people make it through. But maybe I would imply conspiracy since I'd imagine the people at the upper levels, that designed the process, have at least noticed that it's biased in favor of young, recent graduates able to give extra time to the company.

It happens all over the place all the time, if you don't stay late you're "not a team player". Of course your employer isn't going to say you're fired because you're a parent, unless their attorneys are bored. That doesn't make it any more moral to discriminate based on proxy metrics, like how much of your life you're willing to donate to an entity that cares about you only to the extent you're making them profit.