Something I meant to mention in the above, and it's an important point: women have their full complement of eggs pretty much from birth. No new eggs developing over time. They hang out in the ovaries waiting their turn for release, but they are already there. This is one reason why a woman who wants children someday needs to be aware even years in advance of how she treats her body. Men got the better end of the deal in many ways -- unlike eggs, sperm are replaced regularly, so they are always "fresh."