I have a slightly different take on this.

I worry less about the age and more about power. Was he an authority figure, was he experienced enough to manipulate you, was he physically overpowering, was the event against your will?

These sorts of questions are key, I think, and only you can answer them. If you answer yes to any of them, it could be abuse.

Regardless of the label, clearly you have some emotions associated with the event that need to be worked out. You might consider talking to a therapist.

Cyran0