Thanks for all your replies! I'm glad to know I am not out of my mind to feel uncomfortable with this.
Yes, he did talk to me about this, and I am proud of that fact. I am a single mom, bringing him over here at the age of 12 to be with my partner who is British. I know he doesn't tell me everything, but I think we are pretty close.
She is 16, a bit young I think. I did not speak to her about it, but I was told her mother was onboard.
In the end, after some consultation, I told him that it was too soon and that later on, if this are still going well, I MIGHT consider it. I told him that I wanted to get to know her more, that a relationship is a merger of families not only two people... Blah, Blah. Blah. Cliche but true. Later on he said he didn't really expect me to say yes.
He was good with that. Maybe he felt a little pressured too. I think they are both 'beginners'.
I really don't mind if she has been around for a while, and seems like she will be around for a while more...It will be more special then too.
But now is just too soon.