WHAT?! no no no no no.
Before you dole out advice, please be sure you actually understand the law.
If you gift someone an item you transfer ownership to them, e.g. if I were to gift you a mars bar it would become yours.
It is 100% legal for an under 18 person to own a RIF, they just can't buy one. THERE IS NO LEGAL RESTRICTION ON OWNERSHIP OF A RIF, only sale, purchase, manufacture and import.
So when you say they're 'my guns' if your mum/dad/uncle/jimmy saville has given them to you, then they are yours.