You said you had a brother? Could you not use your brother to vouch for you to prove you are who you say you are to get your birth certificate and then from there you can get the rest of your ID.
Or if like you said, the wallet never leaves the house. So clean your house and find it like Greylocks said.
I personally do not care why you do not have ID. However, I do care if airsoft rifles gets into the hands of minors. I'm not saying you are a minor but you do not have anything to prove you are 18+