On a general basis, we think the age restriction on roleplaying is based more on when a person is capable of acting/writing out a role than on some number. There are no doubt children of eight years more eloquent than those of sixteen. People mature differently. We don't think a precise number can be put on when it works and doesn't work.

But there's also the restrictions Mahz mentioned, like the need for parent/guardian consent to join if under a certain age. Such a number rule is in place to both cover people's sixes and to be sure that someone considers the individual old enough to be able to do it.

Granted, we suspect that LARPs might be easier than PbP RPs for the younger ones.