I am worried that, having never had a serious relationship (as you mention earlier in the thread), you might not be prepared for how much work maintaining a relationship actually entails. I get that you are worried about getting older and your perceived timeline of when things should be done, and I dont see any point in trying to persuade you that you are setting unforgiving standards for yourself. But it seems to me like you imagine that as soon as these things are done, crossed off your list, then you can just take it easy.
To be honest, Im pretty sure its the other way round. That is when the really hard work starts. Keeping a marriage going, even without the added (huge) pressure of looking after children, is no easy call. Even when both people are feeling happy and fulfilled and validated and all of that, and you have a truly deep connection, its still a hell of a lot of work. So my advice? Enjoy what you have now. Enjoy being completely free to make decisions, just for you. Take some risks, make some mistakes. Do all of that stuff because when you commit to another person, especially baby people, you cant do that any more.
Your ovaries will be fine. You have at least ten years of not even having to give them the slightest bit of thought and you will still be able to have far more children than a person could reasonably want. Ten years is a long long time. You were 12 ten years ago.
But if what you really truly want is to get married and have babies? Dont go to grad school. It is hard and lonely. Go online and find someone who wants the same things that you do. They exist! A friend of mine, 24 at the time, went online and chatted to only one woman. He told her he wanted a wife, a baby, a house, a volvo. The whole package. She said that so did she. A week later they dated, another week later they moved in together, a year later their son was born. Three years later they are very very happy. Grad school will not get you a husband, looking for a husband will. And then go to grad school.