My DS didn't roll until 2 days before he crawled which was around 7 or 8 months. And of course once he was crawling properly, he didn't end up needing to roll hehe. He then was walking on his own at 11 months.

Looking back, it was fantastic that I could sit him on the floor and he wouldn't go anywhere! LOL. DD on the other hand rolled everywhere, and it was a big pain!

Try not to worry. They do things in their own time