Welcome to PT! My Pouncer was 10 weeks when he came to me, but he still liked to suckle... he even tried to suckle off our male cat, Allen! After many months Pouncer finally gave it up, but occasionally he'll try to bite my fingers when he's really hungry. I take it as a form of suckling too.

Like Karen suggested, if you continue to push him off, he'll eventaully get the idea and stop suckling.