[catminou]

Pilot but trained for ATC in my 20s.

I assure you the mental picture you need to keep in your head as a controller is far more taxing than single pilot operation when you are primarily concerned with your own separation. A controller can be managing a 1 to 2 dozen aircraft, dealing with pop up IFR, flight following, traffic advisories, handoffs, etc. There's a reason you get a mandatory break after 2 hours.

[dsfyu404ed]

It's not about the mental task. It's about selecting for a demgoraphic group that's more compliant and less likely to take risks. They want to lessen their chances of having egg on their face because they hired some young cowboy who, when faced with some impossible set of bureaucratic constraints decided he'd shirk whichever one of the conflicting restraints they didn't like rather than just take the KPI hit.

The under 30 crowd has a lot more of those types than the over 30 crowd.

[ElevenLathe]

This can't be the reasoning because the policy is to select /for/ under-30s, not over-30s.