Like others have said, don't waste tokens on anything less than 5* players.

At lower levels I turned over my entire squad every season - and I've never bought a token - so i didn't worry too much about age until I got to around level 5. Just avoid players over 30 as they might retire on you and deprive you of the much-needed resale money. Even at higher levels you can't train a player fast enough to keep him useful for more than 2-3 seasons (unless you're buying tokens)