I never know when my first one was going to start because I never had it explained to me. (It was a bit traumatic to say the least, I literally thought I was dying I had no clue what was going on)
Anyways fast forward a few years and i can usually tell almost to the day. I get very moody and emotional due to PMS. I also bloat up and sometimes get zits on my face or ulcers in my mouth. I'm just weird like that, everyone is different.
You can get them before. Basically cramps are the euterus muscles expelling the lining. After giving birth 4 times I can say sometimes it seems similar to childbirth contractions!
After a while you can kind of sense it. Your body starts following patterns, emotions may occur, plus if it's regular, you can estimate when your next one is.
Once you start, it'll be irregular (probably) but it gets easier to track as time goes on.
Girls can get them at all different ages. I got mine at ten, some get them in their later teens. Don't rush it. You probably have plenty of time to live with the beautiful utter heck that's periods. Don't sweat it. :-)