Put my mind at ease

My son is almost 6 months and has not rolled over, he’s been sleeping on his tummy since he was 12 weeks old (dangerous I know but that was the only way he would sleep longer and we just check on him to make sure he’s okay) I’ve tried rolling him over myself to show him how to do it but he just looks at me as if I’m crazy lol. He’s a bit chubby ( I must admit he does like his milk). I heard that at this age they should be rolling over, so should I be worried?