This is a very interesting thread, that has me looking back at my relationships. I am not as gifted as your son, but I have to say that I always felt much older than I was. I truly didn't feel my age and almost all of my friends were older than I was. No one I have ever dated was less than two years older than me and I truly felt the same age as they were. Obviously, looking back now, especially as a parent, I see risks with that. But, I think the only thing that kept me from a really overwhelming situation was logic. I was very aware of what the consequences of certain actions would be, long term. And so I would suggest having an open, warm, concerned talk with your son that balances both the emotional and logic. Tell him that you trust his instincts and that you can see why he would be so interested in this woman. And then carefully state your concerns. He seems, from what you said, mature enough to take your comments and process them. See what he thinks of the conversation. And then, if things still concern you in a few weeks, readdress it with him. But give him the chance to take ownership of the situation. BTW: you haven't said if he is living at home with you or if he is living on his own at college. If he is living at home you obviously can have more control of the relationship.
Like other posters, the thing that concerns me the most is the woman herself. The main red flag IMHO is that she was engaged to someone when she began having a relationship with your son. If she did that to her fiance, then your son should be aware that she could easily do that to him. Again, I think this is something you might *carefully* mention to your DS as something he should take into account. You might mention that he should be on the look out for other things about this woman, like her friends. And, I would definitely make him aware of the laws about relationships between teenagers and adults. If he decides that he'd like to get to know this woman better, then you may just have to trust him, right up until the point that you see something unacceptable, and then you will need to get more forcefull with your opinions.
