Yes to the wait-and-see. Just have to mention, though, that the available research does not currently support crawling as a necessary step in brain development. Crossing midline and visual-motor integration, of course, are both quite important, but early walkers-who-skip-crawling generally find lots of other ways to cross midline without special treatment.
I have plenty of training and clinical experience in child development (so I do have some idea of what is "normal"--and it's a pretty broad range), and I, too, had to resist the urge to continuously mentally-assess my children. If you want, keep a monthly (don't overdo it!) journal of interesting milestones or anecdotes about him, in the event that it might be useful retrospectively, but put most of your energy into enjoying the innumerable moments of discovery and accomplishment that he is experiencing every day. You're clearly spending lots of focused time with him; he will show you what he needs for stimulation.
My take home on the every child NEEDS to crawl research which I base from my experience as parent of a child who had developmental delays in learning to walk as a toddler. Is that children who on their own go right to walking there really isn't a big issue with. But kids who have developmental delays and need intervention, should be taught to crawl before they are taught to walk. Often because crawling is one of the best ways to strengthen core muscles that make walking possible.
As to the original posters question. At 18 months is still very hard to tell if your child is gifted. You child defiantly sounds advanced in a few things, and certainly not behind in any milestones and must be a joy to see him learn new things. But nothing particular stand out to me but it's still a bit young for figuring this out. Not sure you need 3 more years, I could tell when my son was reading at 3. Kids are all different, they learn different things at different ages. Keep in mind that gifted kids aren't all alike and have different strengths and weaknesses and learn things at different ages.
