I was in a similar situation three years ago when I was in my 40's and he was 52.
I wanted to get married, he wasn't sure. It came to the point that I wanted to get married before it was too late in life, we're not getting any younger, and wanted the security of a husband, and to take care of each other as we age.
Probably similar reasons as yours. I get it.
I saw a program and it was about men who won't commit. It said you will probably know each other as well as you are going to, and he either will marry you, or he just doesn't want to.
So I gently told him that I wanted to get married, and if he didn't want me as a wife he needs to have the courtesy to let me know. I said think about it for three days, and if I don't hear from you by then, we can remain friends, and I left, did not call, email, etc. It was hard, and stressful as the minutes ticked on!
He called me and asked me over, I went over and he had a 1 carat diamond Marquise cut engagement ring.
So I think maybe an ultimatum is in order, he may never be "ready" but you do have a right to a yes or no answer, and he shouldn't string you along.
Good luck I know it's hard to live in that in between world.