Your boyfriend may be so happy with things as they are that he is anxious about making the change that a wedding creates. This romance is intoxicating to you both. He may wonder whether you two can make the transition to everyday married life. It is certainly going to be different when you two are dealing with day-to-day issues like who cleans the bathroom, who does the laundry, and how money is used intruding on your idyll. I don’t wonder that he wants to hold onto what is.
I think it might help if you stopped talking about a wedding and started talking about each other’s expectations for marriage. You are both in your 50s and are undoubtedly somewhat set in your ways. Neither of you has experience with the compromises that come with married life. Believe me. There are lots and lots of compromises.
Talking about a future life together is a way that couples learn more about each other and start making those compromises. Even something as ordinary as talking about what kind of couch you want for your home can highlight differences and create a way to talk about how decisions will be made. Once both of you feel secure that your romance will survive the transition to marriage, my guess is that wedding planning will happen quite naturally.
I wish you well.