Bloods aren't really fast growers like carpets, retics, and Burmese, but they're not especially slow either. I believe all of my adult short-tailed pythons grew to about 40" at two years old. In the third year, I've found they go through a growth spurt partly in length, but also in girth. This is when they'll get that nice, full-bodied, "classic blood python" look. When they reach 3 years old, their growth slows down a lot, but they'll keep getting longer. And fatter if you feed them too much, so it's important to feed them significantly less when they reach full adult size. Even with my babies, I occasionally skip feeding them for a couple of weeks to give them a rest and let them use some of their fat stores.
ps. Why a male rather than a female or a pair?