My ds is nearly 14 weeks old and 17lb and very long. When he's lying on the floor he makes no effort whatsoever to roll to the side at all. In fact, he just tends to lie still apart from waving his arms to grab the dangly mobile above his head.
I'm not at all concerned because I know babies develop at different times, but I'm curious to know if it's usual for bigger babies to be slower at moving themselves. His peers at the postnatal group are all smaller and seem to be moving much more, some rolling over.
As I said, I'm not concerned at all, just curious to know what other big babies' development has been like.