For the first two years of their lives, ball pythons put on the majority of their growth. Expect your snake to put on 2-3 inches per month for the first year or so, 1 inch or so a month in its second year and more like half an inch a month for it's third year. Expect the snake to Dramatically slow down after that.
Snakes seem to grow in spurts too, so don't feel like your snake is falling behind or getting ahead.
Females also get bigger and grow faster than males.
I would say feed your young ball python once a week until it is 2 years old and then back it off to every two weeks. It should grow at a safe, healthy rate on that schedule and live a long and happy life.
