My DS was 13mths when he started walking and was 8-ish mths when he started to crawl. He will get there when he gets there - it isn't a problem. He is obviously quite happy to do what he is doing because it works so well for him - I have noticed that with some babies they tend to achieve their milestones when they need to kwim? So you may find that when he gets frustrated that he can't do something because he can't walk to it, he may start to put more effort into walking kwim?