depends on how much you feed it. It could take anywhere from 3 or more years for a snake to reach adult size. Not all snakes are garanteed to get that big anyway.
I too would have to say i have had to spend a lot of time with my bredli to get her as placid as she is now. Would have taken me 4-6 months to get her to a point where I can give her to someone for a cuddle and say that she most probably wont bite
I would have to reccomend that a diamond would be a good choice for a first snake although they do require UVB.