I wonder what happened in previous relations that he was in. Since he is 15 years older than you, I figure you are not his first girlfriend.

The best predictor of future behavior is past behavior. Knowing something about his past come be very illuminating. There's a reason why he's single and fancy-free at the moment. If he talks about past romantic failures, listen for the message between the lines. Always assume that what a person tells you about their past is heavily edited to make them look good, or not so bad.