QUESTION: Full grown RTB

[kdnash82]

There is a shop here that has a rescued red tail. They are asking for $100 which is the adoption fee. It's about 6ft and male and was told that he'd probably grow to be another ft.

I held him and he seemed to have a good temperment. The guy said he eats rats or rabbits and was in good health.

My question is, what are disadvantages to buying a snake that's already fully grown, to buying a yearling?