My daughter never crawled either (she's now 23) .. at 8 months she was literally walking all over the place! I thought it was "great" although tiring, until I learned years later about proper brain development and the extreme importance of crawling and how it assists the brain in its wiring and development.
I agree with Rachel K... I would do anything I can to "play" crawling with your son as this is extremely important. As an adult, there are exercises one can do to assist this "crossing over" of energies in the brain, interestingly called The "Cross Crawl" technique. When energies are not crossing back and forth for maximum communication, the person is considered to be in a pattern called "Homolateral" meaning "same sided". This patterns interferes with all levels of development.
You can google "cross crawl" and get lots of information. I just did and found this link which has scientific support for what I am saying here. It is NEVER too late to assist these nerve cells to reprogram, so no worries, just begin to do the exercises. My daughter had some difficulties in school for YEARS with focus, attention and other issues, and I was able to test and determine she was homolateral. We actually began again with crawling! Truly! (she did this at age 17) along with doing the cross/crawl technique and she is a happy graduate today of the University of Miami :-)
Here is the link: http://headbacktohealth.com/Cross_crawl.html
Enjoy!
hugs,
A. F., R.N.
www.amyfreundbodytalk.com