Two of my three never crawled. So I don't think not crawling per se is a problem at all, although some people believe that crawling is necessary for stimulating the brain-- I can't remember the details. Anyway, that's unproven. And I have two three-year-olds here who never crawled, and they're fine.
Our Early Intervention checklist puts as a red flag a baby who hasn't achieved some form of independent mobility by a year old, whether that be crawling, cruising, intentional rolling, scooting, or belly-crawling, or whatever. My DD2 for example hitch-kicked herself around with one arm and the opposite leg, and my DS was a butt-scooter.
By intentional rolling I mean that they roll on purpose to get where they want to go, like babies who see a toy they want and roll over and over on purpose to get to it.
The reason we want to see mobility is because a baby that's not mobile in some way is being held back in his exploration of the world and therefore in his cognitive development. He's not able to get around in his world and get his hands on the things he chooses to be interested in, and therefore he might be missing out on chances to learn new things.
So I think that if he's not getting around in some way, whatever way, by his birthday, I would consider looking into an evaluation. But honestly, most of the babies who have these little extremely minor "delays" are really just running on their own unique developmental timetable, and catch up on their own just fine with patience. Some of them are concentrating on other tasks-- learning to understand language, for instance-- and will return to working on motor skills soon. Others are just unfolding at a pace that is a bit off the average, and yet they're perfectly healthy normal kids. But a few can really benefit from some extra help, and it's hard to know for sure which kids those are.
Can he pull himself up to stand? If he can do that, I would be reassured.
So I would give it some more time. But if you're worried, you can get the eval. Talk to your health care provider. Or you can call Early Intervention services in your state-- the eval is free, they come to your house, and the services themselves are optional, meaning you can change your mind later if you want to.