Hi Op, please take a deep breath, your son has done NOTHING WRONG, he has been respectful to this girl and polite.
You are possibly projecting your worries rather forcefully.
Now is the time to warmly talk to him about what a nice, loving relationship looks like, let him know you know about his friend and would like to chat to him about her and relationships.
Talk openly about respect and consent and the absolute red lines of behavior, ie no pushing her to do anything however much he may want to, no inappropriate photos and no discussing with his mates!
Say you will happily welcome all his friends home including this one but he MUST be open with you, be very calm and smile.
Talk openly about the age of consent and why, (unwanted pregnancy, stds, legal age etc) But say if he were to have sex regagrdless sometime in the future you would rather he told you and wouldn't hit the roof! Then you could discuss issues then.
Talk to him in a non judgemental way but really explain the issues around relationships too young, remind him having girl friends is normal and fun, especially without the complications of sex!!!
Educate him to remain the kind respectful boy he currently is in relation to women, put a womans view, tell him what girls want from boys and how they want to be treated, tell him he will be adored if he treats girls well, that should appeal!
I have a younger DS and worry about making him into the type of man that respects women, as so many don't, so l talk a lot to him about others point of view and how his actions make friends feel.
I also pull him up sharply when he behaves inconsiderately or unkindly and discuss it with him, usually he soon sees the effect of his behavior and gets the message.
Please put your strong feelings aside or you may drive your lovely son away, tell him you trust him to behave well, then educate him on how to do just that, and welcome this girl but also put down fair ground rules.