What a lot of people do if they are enamored of an underage friend who is not amorously attracted to them, but who likes them or loves them in another way, is to cultivate the friendship with that person AS a friendship.

This may sound like torture, but the friendship vibes you receive are the balm that eases the pain. This is called having a Young Friend (YF; though not everyone is madly in love with their YF). It's legal and it's the best form of love that some people ever experience. Despite its physical frustrations, it is much valued.

You can't plan everything in your life rationally, and sexual orientation is a notorious wild card. If you make sure your own, God-given capacity for love is being used in the best way your biology, your spirituality and your society permit (which doesn't deny the opportunity to support legal changes that might be beneficial), then you are on the right path.

Of course, any time unrequited love is too frustrating, you are not tied to the point of having to stick with it. Just don't be cold and leave the poor person wondering what they did to offend you and lose your friendship.