well, I'd refuse to move in until these things are discussed. At a similar age, I told the now DH that I wanted to either have a child or be pregnant on my 30th, and I wanted to be married to that child's father. That was the deadline, if it wasn't going to happen with him, then I'd best know so that I could find someone else.
You don't need to discuss names, how you will parent or what colour you'll decorate their bedrooms, you do need to discuss how you will own this property, the wording of your wills, taking out life insurance to cover the mortgage for the other one in the event of death of one of you, will you get married and have children, do you want a similar number of children, will you be able to afford the mortgage on one wage during a maternity leave(s) and/or would you want to be a stay at home mother.
Perhaps start ask him how long he imagines living in the property you are thinking of buying, and therefore what else will need to be funded during that time. (Know a lot of couples who bought properties in their late 20s, without even thinking if they could afford to take a maternity leave year in the next decade, then getting stressed in their early 30s when they got pregnant that they couldn't afford the mortgage without working full time)
Personally, I'd refuse to take out the mortgage until 10 year plans have been drawn up. rent for a while with him, that's only a 6 month commitment, not 25 years. (Hell of a lot easier to get out of if he's not committed to you.)