My cat Spyder was just the same way. All of his brothers were eating at 4 weeks or so, but not Spyder, he just wanted mamas milk!
Well by about the fifth week I would start placing a little bit of the food in his mouth so he would get the idea, then he would eat some but I would have to do this at every feeding time, sometimes he would eat, sometimes not.
Still at 8 weeks, when they could be given to new homes, I was still getting him to eat this way!
So I kept him (and his brother Chuckie, but not for the same reason) I was afraid to let him go to a new home with his eating problem...but he finally adjusted to eating on his own (at about 2 and a half months old)...and now he's the total opposite (he's 3 years old now), I can't keep him from eating, LOL!!!
Maybe your kitty just needs more time, but if you think there is a real problem, by all means have him checked by your vet.