Absolutely normal developmental progression! Many babies crawl backwards before figuring out how to put it in drive. Some never go forwards, and get where they're going by crawling around in reverse. His next step will be either crawling forwards, or sitting and scooting (which my daughter did, never crawled) or maybe even straight to pulling up to a stand/cruising. At 7.5 months, he's right on schedule. My daughter didn't scoot forward on her butt til she was a year old, and didn't cruise til she was 15 months (then walked at 16 months). All still completely developmentally normal, and I never worried about the late walking (I rather enjoyed it, it was one less thing to worry about, a one-year-old careening around on hardwood floors). When she did walk, she never fell or had any bumps on the head or anything, as she'd already acquired her spatial awareness and well-developed motor control. To get back on subject, your son sounds like he's doing fine and will be crawling or cruising straightaway. Enjoy the calm before the storm, he'll be leading you on a merry chase in no time.