According to a study published in the scientific journal Pediatrics, the average age at which girls get their first period is 12. From here and into the teenage years, periods tend to be irregular. Because the body isn’t considered particularly fertile at this stage, it’s not necessary for your period to find its rhythm. It’s not until your 20s that your period, even if you’re not taking hormonal birth control, finally gets on an even keel, relatively speaking.
“As one gets a little more mature going through the menarche stage, they start ovulating,” Mary Jane Minkin, M.D., a clinical professor of OB-GYN and reproductive sciences at Yale School of Medicine, tells Healthline. “When you start ovulating, barring anything abnormal going on, you start having more regular monthly cycles.”
With these regular cycles, you also become more aware of your body and possible issues. Painful periods, MIA periods, or abnormally heavy menstrual cycles can give you a heads up that something isn’t right, and you should have a doctor check things out.
When your 30s roll around, periods can get a little haywire again — not only because this is a decade in which women tend to have pregnancies but also because perimenopause can start in the mid-to-late 30s. Although perimenopause doesn’t start until early-to-mid 40s in most women, according to Mount Sinai, it’s not unheard of that a woman in her 30s may experience the very beginning symptoms — the obvious one being a whacky menstrual cycle.