Me and my brother mike used to think up video game ideas when we were in first, second, and third grade... We used to come up with these elaborate drawings of levels, items, and in more than occasion - space ships. It's always something I've liked to do, or on a minimal level - think about. It's fun. It's hard work. It's rewarding. When you finish a level, you finish it, and you feel good about it. Even if it was inspired by a previously created level, you made it your own. I'm not sure if my childhood obsession with legos had anything to do with it, but if it did... I'm sure it shows.
Lately I haven't had time for any level design. To date, I've only completed 3 maps. I have worked on at least 6 seriously... It's tough, but every so often I come back to it and fly around in hammer's 3d view. I find myself looking at maps in DoD, and CS thinking about how the brushes look... so I think a break, for me, is needed. Plus, in my junior year of High School, I have a lot to focus on this year. Algebra II along with Acedemic Chemistry should be enough to keep me busy... I'm not the strongest math student, bu I sure do try.
EDIT: Mapping is a skill that will be with you forever, it's like riding a bike.