Husband doesn't understand...

My husband and I very much want to have children at some point. But I have pcos and hypothyroidism and he doesn't seem to understand that it's going to take YEARS for me to conceive. My doctor has told me that I'm 85% likely to miscarry in the unlikely event that I become pregnant, which is a very low likelihood to begin with. He doesn't even want to start trying until we're 30! Neither of us are really ready to have a baby at the moment, but I'm scared that if we don't start trying soon, I'll be too old (no offense to older mothers, this is just pertaining to my personal fertility) to have a healthy pregnancy. My doctor has already expressed that between the hypothyroidism and pcos, my fertility is terrible and that I might not to be able to conceive naturally at all. What should I do to convince him that we should start trying sooner rather than later?