My DD was "slow" with all her gross motor skills. She took ages to hold her head up, roll over and even walk (at 19 months). I was always worried throughout every stage but have decided now that kids are on their own timetable. She was slow with gross motor but early to talk and always had great fine motor skills.

I recommend a child physio though- we saw one and they are very good at picking up what is just normal "lateness" and what is actually a physical problem. Either way they will give you exercises to develop your child or refer you to someone if the issue is more serious.

Good Luck!