I don't know about a BHP as a first snake for a family pet!!! They have a very strong food response, grow to be really bulky and heavy and aren't exactly renowned for being overly placid. I would go for the classic first-time snakes, either an Antaresia (Childrens, Spotted or Stimsons; don't grow too big, usually quite placid, don't need much space etc) or a smaller carpet (Bredli, MD - get to 2.5-3m and usually grow into fairly placid adults)
Getting an older snake is good in terms of temperament, they are over that hatchie craziness, but at the same time, if they haven't been handled regularly, then a nip from a sub-adult will be worse than from a hatchie! Also, if you start with a hatchie, you can get used to the size as they grow, rather than having a 1 or 2m snake from day one!