As a newbie can I just point out that not everyone that has recently joined this site is a complete donkey, whilst there are a number already here.
What makes you think that some of the old hands do not take on too many games? Pokerguy, ksnake and a couple of others may manage their games properly but what about others who make a move once every three or four days? Do you think that is reasonable?
Then what is reasonable? If you limit the possibilities for newbies who will want to join? You have to have a careful balance between caution and draconianism.
I would suggest something simple.
You cannot join more than two leagues at any one time until 100 games have been completed.
You cannot join more than 30 individual games at any one time until 100 games have been completed.
This way a newbie is not swamped until they have some experience of the amount of work that is involved in playing multiple games on YPI. However you cannot account for stupidity and should a newbie join way too many games after completing 100 then you know to avoid them.
This way some sensible people, who happen to have a coach taking the mickey sat right next to them, are not restricted and feel welcomed by the YPI community - except by ksnake

Remember this is supposed to be fun.

BMBug