At the rate you are losing it at you will need to start thinking about it or you will have gone past it before you decide! Seriously though it is just what suits you, some have specific targets in mind, some don't.
I think a lot depends on whether you have some idea of a weight that you have liked being and worked well for you. As you are a young guy you won't necessarily have that sort of reference point. Anyway it is great to see you are doing so well, especially with college, keep up the good work x