Your fertility drops exponentially after age 35, and the risks for both the mother and child significantly increase. And since it takes ~2 years to make a baby,

Your fertility drops exponentially after age 35, and the risks for both the mother and child significantly increase. And since it takes ~2 years to make a baby, ideally you should start having kids no later than 35 - 2k, where k is the number of kids you want. And you probably want at least one extra year in case anything goes wrong, which it often does. IVF and egg freezing, while useful tools, don't really magically change this formula in any meaningful way.