I know a number of graduate students who are married. Some of them have small children. I'll admit that they are mostly male, but then I guess I mostly know male graduate students lol.

It does become an issue about when is a good time... The stats do change significantly from 35 - but still, is it a a good time before grad school, during grad school, after grad school (before getting a job), shortly after you get your first job???? There are pros and cons for all of those, I think. So really, when it comes down to it, I think it is more about what seems right for you and then making it work.

Graduate school is more work than being an undergrad. If you are in the US system then you have 2 (or possibly 3) years of coursework and your funding is dependent on your doing those courses. You will probably also have teaching requirements and so there is a lot of work to be staying caught up with and a lot of writing to be staying caught up with too.

Your fourth year on when you are basically writing up your dissertation there is more flexibility with respect to you basically doing your work and not so much needing to be at a certain place at a certain time (as with coursework). You could work from home a little more... But one can't both attend to kids and write... So things could be a little tricky, yeah. Basically... I think you would need him to be willing to do at least half of the caretaking stuff for it to be feasible. The guys I know seem to take half of the caretaking stuff and while it is hard for them they are managing. Instead of going out drinking with the others they are home with the kids. That being said it isn't social suicide because there are others in the same boat and you can always do dinner party / family friendly activities etc etc.

Personally (just me personally) I wouldn't panic until the age of 30. I'd want to get cracking then because the stats do change at the age of 35. Interesting to think that the stats USED to change at the age of 30 but modern medical advances etc etc have resulted in 35 now being considered significant. There are a number of women who do have healthy pregnancies after the age of 35 even and by the time you get to 35 the stats might have been pushed back to 40. I think you are worrying about this a little too soon... Once you have your first job (with maternity leave etc and decent health etc benefits) is probably the best time. I don't think they are allowed to ask you about your plans to have children on hiring committees in the US at least.

But you do need to do what seems right to you of course. Do you have a doctor who you can trust to talk this over with? Might be nice to get some reassurance / honest advice from a health professional who has seen the kinds of problems etc that are concerning you. They may also be able to consider how severe your PCOS is to determine whether you are likely to have trouble conceiving and whether there are potential ways around that (e.g., preembryonic implants which potentially MIGHT be covered on some health insurance plans if not graduate student health insurance plans OR financially feasible with two incomes.).