He's never had a long term relationship, does it matter?

I wouldn't be worried. At that age a lot of guys haven't been in long term relationships. I say give it a shot and hope for the best. My husband was 19 when we started dating and he had never been in a long term relationship (his longest relationship was 3 months) and here we are 11 years later very happy and still together. Just because he's never had a long lasting relationship before you doesn't mean it won't work out so if you like him, go for it. :)