As long has his mobility is good no need to worry. My first baby skipped crawling, I started putting him in a Walker but he will climb down from it and rather push d walker while he walked. Rather than crawl, he will roll on the floor to get what he wants. Different baby different strokes. Your main concern should be his mobility (can he hold is neck, can he move his legs and hands, can he sit). If he can, no cause for alarm.