If he's taking that many steps alone, it's only a matter of time before he continues to gain confidence and be all over the place! Even though it feels on the late side, don't stress, sounds like he's fine and will soon be walking. Think about it, you didn't see those first 5 steps day of the appointment coming, just like you may not see it coming when he just starts walking full time one day! Consider his personality when you're encouraging him to walk - does all the applause and cheers make him shy away more? Maybe he needs you to pay very little attention to his steps before he will do more? I don't know this, but it may be a possibility if he's an overly-cautious kind of guy. The reward for his walking is his freedom (which he will soon discover) and doesn't have to be clapping etc. from his parents. Unless that helps him of course!
Good luck! My son is 15 months old, and started walking right before 14 months. He had a few days of walking maybe 5-10 steps at a time and then after about 1-2 weeks, he was walking full time. During that time, he just got to doing more walking/less crawling with each day.