Whilst their PA is a good measurement when recruiting players or developing youngsters it's not the only measurement worth using. Obviously they won't reach this PA if their hidden attributes are poor; Professionalism, Ambition etc or they've had poor development up to their young 20's.
I've seen lots of regens with excellent attributes with PA's as low as 160, so it's not always a good thing to exclude players lower than 166 for example
But generally speaking, with prior knowledge of a lot of good FM youngsters, i look for a minimum PA of 175. Someone is gonna say You can't see PA without cheating!!! and they'd be right, but with years of FM experience you generally get to know major players CA and PA. I usually compare the scout report text to my current players anyway to gain an understanding of the new player.
Well, have a look at the following teams and see their lowest PA youth players:
These teams have rather good youth team academies, and you will note that they have youth players with PA of -4. Therefore, what you state as minimum PA should be far, far lower. Remember that many of those teams actually sell youth players to lower league teams. Just because somebody is at a mega team's youth squad does not mean he is the next ronaldo or messi.