Both my 2 crawled within a day of each other age wise (and that could be put down to the fact that dd who crawled "first" was born at lunch and ds who crawled the day later age wise was born late at night!). They both did it a couple of days after they turned 6 months!!!
Every bub is different but I think it's pretty amazing that they both crawled all but exactly the same age! smile
Friends baby hadn't even started to crawl when dd was walking (running), she was just happy to sit and be carried everywhere. Lol.