The short answer is: while that may be the Mercs policy, it's not our policy. Me and catal pay the bills, so we can refuse anyone we feel like refusing.
The longer answer is what Ghostwalker said. Alllowing minors to even post (as we're a closed community, we're a little lax on things like language and et cetera) would open us up to a whole ton of legal junk. And as much as I love costuming and believe that HHS is a much-needed resource, legal hassles are just not worth it.
Once you turn 18, feel free to sign up.
EDIT: We do have a clause that allows minors as long as their parent or guardian is a member in good standing of the community. So there's that.