The above link could be helpful to understanding your situation.
You can set Age Restrictions, Spending Limits etc from the Parental Controls. But when he goes to play online, his age will prevent him playing any game that has a higher Rating.
You also fund the Master Account (Yours) and give your Son a spending Limit. He won't have a PSN Wallet for money, when he buys something via his Account, it draws the money from your Account.
Anyways, check out the Link... useful details there.
Ava
