Normally I would agree but with experience in this kind of thing and going through both sides of the coin I have to disagree.

You're not just telling her you're gay here, you're telling her you're gay and got involved with a minor. The shock factor doubled here. The low blow route works wonders. Really a age is not important, you got together because you two wanted to be together. Making that decision and continuing to grow with you already makes him a adult. Others don't see it that way though and freak out with the thin lined details. Just my thoughts bro, you know I support you.