Somewhere in your twenties, usually right after someone asks when you're having kids, you've probably also heard the reassurance: you're young, you've got time, no need to think about any of that yet.

It's a reasonable thing to believe, and the time part is mostly true. But "I'm young" and "I don't need to think about this yet" aren't quite the same statement, even though they tend to be said in the same breath. 

The women who feel most in control of their options later are almost always the ones who got the information early, while it was still just information and not something to solve.

So whether kids are a definite, a maybe, or a firm no, here's what's worth knowing now.

Your twenties are the widest part of the window

This part of the myth is true.

According to ACOG (the American College of Obstetricians and Gynecologists), your peak reproductive years sit between your late teens and late twenties. Fertility starts to gradually decline after 30 and picks up pace in your mid-thirties.

The reason comes down to your eggs. You're born with every egg you'll ever have, and as you get older both the number and the quality slowly come down. So your twenties aren't just early, they're the stretch when that supply is at its highest and its healthiest.

Four things worth knowing in your 20s

None of these need to be acted on today. They're just the basics worth having in your back pocket, so nothing about your own body ever takes you by surprise.

• Your cycle is a signal. A roughly regular, manageable period is a good sign your hormones are doing their job, and cycles that are very painful, very heavy, or all over the place are worth mentioning to a doctor rather than pushing through.

• It helps to know two common conditions. Endometriosis and PMOS (formerly known as PCOS) are both common, each affecting roughly 1 in 10 women, and both are very manageable once they're known about. The usual signs are periods that are very painful, very heavy, or irregular, so if that sounds like yours, it's worth a conversation with your doctor.

• Ask for a yearly STI screen. Chlamydia and gonorrhea are the most common preventable causes of infertility and usually come with no symptoms, so the CDC recommends a yearly test for every sexually active woman under 25. Caught early it's a simple course of antibiotics, left alone it can quietly scar the fallopian tubes.

• Keep up your yearly checkup. Making your annual well-woman visit a habit is one of the easiest things you can do for yourself, and from 21, ACOG recommends a Pap test every three years to catch any cervical changes long before they could become a problem.

The myth isn't really about age

Knowing how your body works has nothing to do with having decided what you want from it. You can track your cycle, keep up your screenings, and understand your own fertility while having no idea whether you want kids, when, or with whom, and that's completely okay.

When you unpack "I don't need to think about this yet," it usually isn't about being young at all. It's the quiet assumption that thinking about fertility means worrying about it, so it's better left in a drawer until it's relevant.

We'd gently flip that. Thinking about it early is the thing that keeps it from ever becoming a worry. The difference between having options and having urgency mostly comes down to information, and the timing of when you got it.

So what do you do with all this?

Less than you'd think, and that's sort of the point. You don't need a plan or a panic. Get familiar with your own cycle, keep up with the routine checks, and remember that your twenties are your most flexible years, not your final ones.