To try for a baby or not to try.....

I am 18 and personally would love to have a baby in about a year or two. My SO wants to essentially pause our relationship (and by pause I mean hold off on kids, wedding, and moving in together) until his youngest finishes school. That's 8 years away. I understand that his kids come first but I feel like 8 years is a while. He is already 15 years my senior and I don't want to wait forever to have kids haha. I'd like to have my kids when I'm a decent age. However, he's insisted that if it happens unplanned then it happens. I don't want to I guess be an extra burden by getting pregnant but at the same time it's something I really want. he wants it too just later on. Do I agree with him and wait or try and convince him to have a baby? I don't want to mess this up. Thoughts?