Well, of course he has a calling; the only question is about whether it is to the priesthood. It is very common, though, for men who become priests to first have the idea to occur to them around fifth grade or late in high school. Many of us get a first inkling about our calling at that age.
We are never too young to be called by God for a particular work. If this young man has a desire to know more about the priesthood and to become closer to God, I would tell him that he should consider pursuing that desire to be his call for right now, even though he won’t know where that will lead him by the time he’s a man. What God has in mind for tomorrow is tomorrow’s concern, and can be left to God. Today’s call is enough for today.
In other words, God may be putting this desire to know more about the priesthood into him as a first step to becoming a priest. He might also be lead this way so that he will be in a position to be encouraging and knowing with a friend whom God will ultimately call to be a priest. He may be called to be a father to priests or religious. He and one or more of his friends might all be called to the priesthood. We never know. As time goes by, then, let him know it is very important that he be open to what God wants, not what he wants, what his parents want, what he friends want, and so on. It is important that he let his friends know this, too, about their own lives. I don’t mean that you let him know this in a lecture. I mean to include in your family’s prayers for vocations the prayer that all will have the courage and openness to follow God’s will for their lives, especially those who are at a crossroads right now. That kind of thing. Live it, more than just talking about it.