I wouldn't. She's only 16.
We didn't have any teen pregnancies in my circle of friends, but far worse, the girls who started having sex at that age developed a terrible attitude towards sex and awful self-esteem issues. Took them over 10 years to get their heads in a better place.
The ones who waited just a few more years didn't have any extreme issues, just the usual girl angst.
From a purely personal POV, it seems to me that sex is not a scarring experience for a 16-year-old boy (or 17 in this case!) but it's too soon for a 16-year-old girl, no matter how smart and mature she seems. Relationships at that age don't last more than a few months. Boys move on. Girls feel dirty and used and start to offer more than they're comfortable with to the next boy in an attempt to be loved.
I mean, you could focus on taking down the patriarchy and societal advertising that makes girls unreasonably feel this way, or you could simply make it harder for your son to sleep with this girl. Not for his benefit, but for hers. If they really want to sleep together, they'll find a way, but if she doesn't totally, definitely want to sleep with your son, you've given her a good excuse to delay until she's sure if it's what she really wants to do.
I also think you should have a Talk with him, if you haven't already. I'm not talking about the conceptive side of things, although that is important and does need to be said. I'm talking about how he shouldn't mislead or pressure any girl into doing something she doesn't really want to do. Feelings can change and there's no guilt there, but he should never sleep with a girl if he knows she thinks he has deeper feelings than he actually has. Etc.