It all depends on the snakes, Some are placid from day one. My stimson from when I first got her at 3 weeks old you could hold her and she'd be fine, never thought about striking or biting anyone that holds her, even when she's shedding.
Each snake has it's own temperament, I know someone who has a Bredli that hates to be touched, even with a snake hook she'll strike and attempt to attack anything withing striking range.
Most snakes generally tend to grow out of the snappy stage, but I guess that you'll just have to take some bites (if he's a biter) until he realises that you're not a threat to him.
I don't know if you've read an old thread that had information to help people with a bitting snake, But there was something in there about, getting a cloth and wiping some of your sweat onto it and placing it in the enclosure, then leaving the snake alone for 2 weeks. The snake gets use to your smell and associates that smell as a safe smell.