Although you are not 21 and therefore ineligible to be a member of the clan, please feel free to send friend request to some of the 4GCers that have room. I have already added you, and have enjoyed our games.
We are a friendly clan and don't strictly play with clanmates only. As I hope you appreciate, rules are rules and they are there for a reason.
Thanks for your interest though. I'm sure we can recommend a clan that does not have the age barrier if you would like.
PSN message me and I will do some research for you.