The signs are a little different for everyone, and as you get older, you’ll get really good at reading your body. Before you get your first period, you may be noticing other changes in your body: Recent studies show that most girls start developing breast buds sometime between age 9 and 10. Some things to look for also are sore breasts, back pain, cranky moods, constipation, a bloated belly and possibly even breakouts on your skin. You likely will not experience all of these symptoms before your first period or the ones that will follow, but you might experience some.