Make players rubbish
 

How do i setup a game so the generated players are 90% crap, 8% ok and maybe 2% actually able to play the sport?

Are you looking to build a league that gets dominated by a small number of super elite players, with mediocre talent surrounding them? The initial creation of the player pool would be relatively easy, but building the foundation of incoming talent to match your distribution would be far more work.

Essentially im making a Veterans league, so min age at like 35-40, upto and including people in their 70s

So i dont want many if any players actually that good.. its going to be an indenpendent setup, nothing real, just to simulate something we have in the UK for older people is walking football (soccer)... so let the old boys stay involved but clearly at a standard that isnt as it could be

i know its all relative but id prefer to actually see the players being useless, so if anything good happens its a nice surprise.

Will this league be running along side other leagues in your save? Or standalone in a save by itself?

You're going to have issues with guys retiring. I don't think there's a way to keep them from retiring en masse every offseason. You'll probably have to do a lot of manual unretiring of players each year.

If you set the PCM's really low (like rookie league quality), your players will have very low ratings across the board.