Genetics definitely come into it when deciding when kids roll, crawl and walk etc. My 3 big kids were more or less the same. They all rolled over at about 3 months, sat at 6, crawled at 9, said their first word around 10 and walked between 13 and 14. There was never any more than 2 or 3 weeks difference in their pattern. But of course I didn't know if they were following a Buchanan pattern or a Gautier pattern.
When Anna rolled at 3 months, I figured I knew what was to come next. But I didn't. When I say she rolled at 3 months, I mean exactly that. She rolled over twice, decided she didn't like being on her stomach and hasn't done it since. About a week later she sat up unaided, at half the age of the Gautier babies and has been sitting ever since. At 6 months she started to shuffle around slowly, not moving far but moving definitely, on her bottom, not on her knees. Now at 7 she's pulling herself up onto her feet when she can, but still is completely uninterested in crawling. I have this sneaking suspicion she's only a short way off just standing up and walking away, completely missing out on the crawling stage, as it would involve the dreaded being on her front that she so detests.
Only time will tell.