The Melting Pot, a great fondue place in Gaithersburg has a great package for parties. Kids (and adults) love dipping meats and fruits...etc. in all kinds of sauces and dips. He can invite friends and the staff is great to work with.
You can never lose with that one day trip to New York City to see a great play, like Billy Elliott or the one with Daniel Radcliff. They have those buses that pick you up and bring you back the same day.
Another great day trip is a (snow) tubing trip at one of the ski resorts. My daughter went on one last year for a birthday party and it was great.
There are all kinds of organizations around here that do biking and kayaking...etc. if he is a real outdoors guy. They usually have birthday packages.
Rockville sportsplex or a large indoor rock climbing party would also be great, followed by a birthday cake (most of these places have party rooms).
If he is really serious about not having a party, any of these things can be done with one or two buddies!
Best of luck and Happy Birthday to your son!!!!!