It can happen. As long as there is no clinical problem, it should not be a cause for worry. Of course, parents have to keep making efforts to make the child walk. This can be done, by putting the child in walker or help the child move a few steps by holding their hands. If the milestones are O.K. as per the doctor, there should not be any cause of worry.
Massaging the Baby's legs gently everyday, gives them strength to walk at the right time.
There can be genetic reasons too. If one of the parent had walked late, the child might also walk late.