Welcome! Check out the ball python care sheet on this website for some good info.
Ball Pythons get to be 3-5 feet, females are larger than males. Generally, they'll grow to more than 3 feet within 3 years.
What kind of snakes do you have now?
Did you already get the ball python? If not, one hint I can offer is to get it's enclosure all set up with the correct temperatures, humidities, and # of hides before bringing your snake home.
Post any other questions you have, everyone here is really helpful.