Hmm - of the sitting, crawling, standing and walking milestones - both DD's were only sitting at 9 months! DD1 had started writing and could ride a 2-wheeler (never had training wheels) before her 4th birthday.

I think it is drawing a very long bow. Many children who are slower to develop in morot skills are earlier to develop talking and other cognitive skills. Babies all develop different skills at different rates.