This child is currently 17 months old this month. however, he is unable to walk by himself yet. what should i do?

Take him for an evaluation by a pediatrician who can start the process. S/he may refer the kid for formal assessment by a physical therapist and do other tests. If the kid was 12 weeks premature this may be simple delay but if born at term this is a definite delay.

Please have his doctor do a complete developmental and physical evaluation; that would be the first step. It is important to know if his development is progressing (can he stand alone and when did that happen; can he walk pushing a toy; can he cruise along the furniture; can he feed himself, etc).