Baby not rolling

My little boy will be 6months on the 9th but seems to have nooo interest in rolling...I've literally only seen him do it once 🙈He is a happy baby and enjoys tummy time (able to push his chest up high in the air and 'spin' around whilst still on his tummy to other directions). We are practicing sitting at the moment and can sit by himself for brief seconds already.Should I be concerned? Is there any other mamas in the same boat?