For members, I'm not aware of any legal restrictions on the age of members and I don't see any advantage in introducing one. Can anyone think of any good reasons to restrict age? For me, if someone has the nouse to set up an account on wikimedia and participate, i think they would be able to constructuvely participate in the chapter and so should be welcomed in.
If we accept under-16 members, then we probably want to make sure that their parents countersign the membership application (or otherwise indicate that they support their child joining the organization). That's not a show-stopper, though.
Mike