Considering your age, I completely agree that you should keep what you have, as long as it fits.
If you're riding on paved trails and no rip-rap, then you can put some pretty light semi-slicks on your bike. My favorite for road use is Primo Comets. They are light, fast, and inexpensive, and give fairly good wear. The trade-offs are, the good wear comes at the expense of some traction in wet, and since they are racing tires, they are not as durable as, say, a Specialized FatBoy. Still, I've used them for years and only gotten one p*nct*re flat with them. And besides, if you want durable, keep your knobbies. Comets come in various sizes, from 26x1.0 to 26x1.75.
http://www.amazon.com/Primo-Comet-Re.../dp/B001F6ZFKI
But any bike shop can get them.