Firstly - is he a baptised JW or just a JW by association/family?
My son has a girlfriend at school at 16. Many would say he is a JW because we as his parents have been JWs all our lives. We are now fading, so quietly leaving. Therefore there are ones who would not know our current position​.
When I was 16 nearly every one of the teenagers in my congregation had boyfriend/girlfriends at school. Some went on to immerse themselves in the JW way of life and some did not.
If you want to know where he stands just ask him. If he is a believer I would recommend research into the cult and do said research together with your daughter.
If he is just biding his time until he is his own man he will need a family to accept him when his own will not.