Thanks for all the replies. To clarify, we have talked about children and he tells me he is not sure, but tending towards not wanting any. I am also on the fence, but am sure that I want to be with him. If he doesn't want kids then fine by me as long as he commits to me. I am 39 so he knows that children with me cannot be delayed a moment longer. What scares me is that he says this now then in 5 or 10 years changes his mind and leaves me for a younger woman. Hence I'd like to be married. The best I can get from him is "I'm very happy". We are just about to move in together- I had big plans to refuse to do so without being married but when he suggested living together I realised that I was not prepared to end it if he wasn't yet ready to marry, and if he needed to take it in stages then so be it. I just wish he was in a place where he wanted us to be married. I am financially secure (earn more than him) so won't be putting myself at risk in that sense. He is 5 years younger and I am his longest ever relationship.
It's a very unhealthy view of marriage - to want it because you are scared of being left for a younger woman. That said, your unease is understandable, because he isn't actually giving you any definite answers at all, even if they are his honest opinions.
I got married the first time because I really loved my then girlfriend, and could easily imagine spending the rest of my life with her. We were happy, but never got over the kids problem (she wanted, I didn't).
Second time round was much the same, although I made sure to discuss kids thoroughly beforehand. However, my wife had always been a live for the moment person, and said that she didn't see herself getting tied down. But after I was sure, I sort of wishywashily asked her something along the lines of "do you think you will ever want to settle down", and that got her thinking about marriage, and then a month or two later, sloshed on my delicious margarita, she said she was ready to become BadLass.
It doesn't really sound like your partner wants to, and I would advise that if your partner is excited about marrying you, then don't marry him.