The only thing I could foresee being a downfall of posting your age, would be so pespective clients may shy away from you for the mere misconception that you don't have the experience because you're younger.
Although this day and age kids can out perform some adults on the computer.
As far as extra stuff to put in the bio, treat it like a remume. Add some hobbies, interests, etc. Unless your only hobby is getting drunk and smoking dope, lol.