Mali Uromastyx- How old when full grown?

I work in a pet store and have become attached to a Mali Uromastyx we call Zig and I'm considering buying her. We do not know how old the reptiles we get are, only that they're "Adult" or "Juvenile". We've had Zig in the store for a while now and she's definitely full grown, but I'm wondering on average how old they are when they reach full size, so I can get a vague idea of how old she is. I'd also appreciate any other suggestions or ideas you may have on keeping a uro as a pet. Thanks!