Can I approach this from a different side? He has two young girls who he knows are getting mighty attached to you. I would hesitate, too, if DS was so attached to a new man in my life. And, yes, I think almost one year is still pretty new. Especially if you're hoping the relationship lasts 10, 25, 50 years.
Another thought is, he may be feeling a bit rushed. By his girls, by your "I love you", by his own visions of a future with a house with more than just him and his girls. I think it's a good sign that he's wanting to slow things down; kind of give every one a chance to catch their breath and look around at what is *now*.
I asked him, "Too soon? For whom? you or me?" He kinda fumbled through it and said, "for you."
So, we talked about it the next day. I accused him of projecting his previous 1 year relationship on me because he wasn't ready to commit to his prior girlfriend. He agreed that was part of his reasoning. He also said, "You have to look into your options. Maybe you will meet someone who has grown kids and is in a similar place as you are? We're in very different places. I'm in the midst of child rearing my 2 young girls. Your son will be graduating soon and your life will be changing. I just don't want you to rush into things, blah blah blah"
He admitted he might be projecting his last relationship onto this one. He's willing to look at his own behavior and feelings and take responsibility for them. I personally don't really see his comment as being controlling. I see it as him bringing up a valid point for consideration. Besides him, you've only had a couple flings after a long marriage. A marriage that nearly reached the quarter of a century mark. I don't see his comments, as you related here, as him telling you how you feel. I see him pointing out that you haven't really seen who else is out there besides him and your ex-husband.
I see him pointing out that your son is almost off to college, but his girls are much younger. In some cases, that might make a huge difference, one that in the first blush of romance may not have been considered. He may wonder if you will later stop, look around and think, "I've already raised my kid. I've already gone through this. I'm done. I do NOT want to raise any more."
Perhaps as you continue to date, it would help to discuss if he's afraid he's your "rebound" relationship and your reasons behind why you think it's not? Or have serious discussions about how you both feel about raising kids - more kids - kids who are not biologically your own. Kids who have other parents who are going to be peripherally involved in your lives because of the kids.