my baby is 6 months old only he is rooling down he is not rolling up is that ok

A. Hello good afternoon !! By 3-5 months babies start roll over like initial roll downside once a while seeing downwards but cant hold their neck,head..,gradually they start roll over downside very frequently and stable(hold ) thier neck and see upward. Tummy time helps a lot for roll over,crawling give tummy time daily 10 -15 minutes which improves ab strength,digestion,roll over ,holding neck,crawling...