I always feel very hesitant to say anything when someone doesn’t confirm their age. I believe it’s ok for people to be together in their teens if they are close in age, but if this is the path you are taking, please use protection.
In your case though, it seems more complicated. I am not a relationship expert (there’s no such thing as a relationship expert) so I can only offer my humble suggestion. It takes two people to make a relationship work, and flings aren’t for everyone. So if you don’t want just a fling.. if you want something more, then this doesn’t look like a good situation.
Some guys use pretty words just to seduce someone enough to have sex, and then they lose interest and move on. If you still want to give him a chance, you should wait a long while (some months or a year) to see if he wants the same thing you do. If he truly cares about you he will still be there. If his mind wanders, then it’s likely because his feelings weren’t that strong to begin with. At this stage, I don’t think you should rush into anything. Wait to see if you both want the same thing.