BPs will constantly grow, however, if you want to go by weight..
Full grown to me is about 1200+g for females and almost 4ft long.
For males, it's about 800-1000g and about 3ft long.
Full grown may not be in a year or two years. Some people wait two years or more to breed females, so that's a good indication to go by. There's not really a set point of full grown. My two year old ball is still a very small boy, but that's just his nature.