Im not sure if there is a viable means to verify an age though. If memory serves correctly, in registration you can just put any age effectively, and the age entry is a age range even. I suppose verification can be done at badge pickup, but that might slow it down a bit and cause conflict, especially with group registration where most of the group wont be around to verify their ages. I think most importantly though, if you are going to mark age on badges, there might be an expectation that a badge marked for a certain age can be used in place of showing ID, and with that there could be an issue with people trading their badges to underage congoers. And if thats not allowed, then Im sure a lot of people are going to be wondering why it is being implemented at all.
These aren't all huge issues and can probably be remedied easily enough, but in the long run Im not sure if is all that worth dealing with either. I think it might just be easier to ask how old they are. You can be indirect about it and ask them where they are taking classes, where they work, or if they drink or something as well easy enough. Its all easy to lie about no doubt, but not any less then it is to lie to registration.