My daughter knew how at about 3 months but didn't really do it a lot until recently

Front to back at 2 1/2 months. She almost has back to front now except for a hang up on the downside arm and she's 4 1/2 months

3 months

7 months I'd say

my daughter does it SO much now and she's 7 months old.

My little man rolled over from his belly to back at like 5 weeks I think. But took him a couple weeks to roll over again. I think he just go lucky hehe then he rolled over from his back to belly at 4.5 months