DO NOT MARRY THIS MAN until you get this sorted out.
And if you think breaking off an engagement is painful, a divorce is far, far worse.
I was very immature and young when I married an equally immature man.
Instead of talking about things like kids, we just merrily went on not worrying abuot the future.
Eight years later, we finalised an amicable, but a very painful divorce because he did not want children.
There is nothing wrong with this. Not wanting children doesn't make a person selfish, ungiving, immature or bad. Quite the opposite. It takes much to be honest with yourself and your partner about such a huge issue and be mature enough to admit to yourself that you do not want to parent.
Explore this man's reasons for not wanting them.
If they are deep seated and really intrinsic to the person he is, you both need to find other people you can be happy with.
29 is young enough to make such a break.
The last thing a child needs is a parent who had to be cajoled or manipulated into having them against their better judgement.
And for every 'oh, but once the baby comes along he'll love it', there's a lone parent whose partner has left.
Babies and children have a huge impact on a relationship. Ideally, it needs to be VERY solid before you start trying to conceive.