If you are worried about it, then it is a potential problem. Not all men have a strong enough ego for this. It is sad to say, and I'm sorry to say it, but it is true. If you are confident that he is strong in this way, it's fine, but if you are not confident, you should carefully weigh the pros and cons.
I know that I'm going to get a lot of flack for this, but I will say the following anyway because this is a serious decision you are contemplating. The worst that can happen is that you dismiss my comments as worthless.
Often in these situations, the man is afraid, but deep down inside is ready. But, he needs to discover this for himself and not have it forced on him via proposal. On the other side, the woman is rightly wanting to move along because of desires to have children. She is correct to feel that things should move to the next level. Hence, often the woman will express her concerns and basically make it clear that it is time to move to the next level, or perhaps it is time to end the relationship. If this is the right guy, he wont want to lose you and will realize that losing you is much scarier than commitment. At that point he might propose, or you might talk and mutually agree to it.
I'm not suggesting you do this, as I don't want the bad possibilities of this on my conscious. I'm just reminding you of things that I'm sure you have seen in other relationships.
I know it's crazy and makes no sense, but human nature does not always make sense.
OK, I'm bracing myself for the retribution coming my way. I can take it. My motivation is the 1 percent chance that my words might offer even 1 percent benefit.