Bonsai take Years, even a life time to grow. You should start one ASAP because you could be passing it on when you die if you take care of it.
After a year or two it will start to look good, it depends how well you train them and how well you take care of them.
I know people who grow them, I dont grow any myself, but I have really been wanting to start growing one as a bit of a hobby.
As far as an MJ bonsai....I dunno about that, MJ grows too fast and probably wouldnt work out so well.