If you got that RTB, you'd have to realise that you are going to have to be responsible for a possibly 10' long 40lb or more snake that can live 40 years. Your son may love snakes, but kids are notorious for losing interest in their pets and it turns into the parent's pet.. now, that may be just fine with you, but think long and hard before getting a boa!

ALL snakes (with the possible exception of the egg eating snake) have teeth. Now granted, most garters are too small to draw blood, these snakes are EXTREMELY fast. They are not normally the easiest snakes to handle, quite skittish usually. There are exceptions, but I'd lean more towards a corn snake (which come in a myriad of color and pattern morphs to pick from at a low price)