Hi!
2' is the very smallest end of the spectrum, and not a good representative of the average. Balls in general tend to be between 3' and 5', with a select few being up to 6' or as little as 2'. Most of the adult males I've seen have been at least 3 1/2'. My adult female is 5', and my adult males are 4'. Gender is no guarantee of small (or large) size, by the way. It's just how things tend to turn out, on average. 
If you want a snake that'll stay 2', check out a sandboa or a rosy boa male. Those species rarely get over 2', especially for a male. If you want a snake that'll live comfortably in a 10 gallon its whole life, a ball isn't the snake for you. Just something to consider 
~jenny
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