hi smow - as you know my baby was born at around the same time, although 10 weeks early. She has only just started rolling over and is not sitting unaided yet. My husband says babies are all as individual as grains of rice - they mostly take around 10 minutes to cook, but some of them are done in 9 minutes, where as some take 11. Is your son or the mum worried? If so, get them to talk to their HV, although i suspect the HV will say just the same as everyone has said