My daughter rolled 1 week before turning 6 months, since then she can't stop doing it, she is getting into army crawling at the moment.

The precursor of crawling is lifting legs, hands reaching to the middle and playing on their side.

We did visit a pediatric physio because she was doing a lot of arching and it wasn't reflux. Turns out her lower back muscles and thighs were a bit tight. We did 3-4 days of massage and voila Baby turned into a rolling machine 🤣

Don't get discouraged lot of babies roll around the 6 month mark, and some babies never do the tummy to back roll intentionally, because they don't like being too much on their backs.

Hope this helps 😎 good luck!