i reckon that he just hasnt learnt to settle himself to sleep- sleep that next sleep cycle
my DS2 still wakes at least 4-5 times a night and he is 18 months
his brother and sister were 3 years old before they could!!
its only a problem if it is a problem for you
he will eventually learn- it is up to you if you employ a method to help him learn or just let him learn by himself
no easy answer- if there was, then we would all lose the lovely luggage we carry around under our eyes !! LOL