4 month old not rolling over and no head control? i never gave him tummy time.. how long can i wait?

A. You can give tummy time after completing the time of three months total head control comes by the age of six and partial comes by the age of three when you put your child on onto tummy time you will see that child comfortably lift the head and roll over can be seen between the time of 3 to 9 months so everything seems perfect as of now