No way of knowing. Many factors could have been played or not played in its time from hatching to now that would affect its size. Didn't you ask the person you bought it from? They should have known.
Check out some of the Leo threads. You'll see how/why sizes vary and ages. Lots of GREAT Leo's here.
Please take some time to ready the stickies about humidity and feeding. Very important stuff.
Good luck with you Leo!!
Welcome to the forum. Can you post pictures of your tort and your set up? Take a look at the pinned threads at the top of the Leopard forum for lots of good info.