Potty Training - what age is considered "late"?

[amldaley]

My nephew is 4 years, 4 mos old. He is not potty trained. He was supposed to enter preschool this year but can't as he is still totally in diapers. My brother and his wife say that they have tried, but my SIL has a "hands off" approach to parenting....she thinks he will learn whatever he needs to when he is ready.

(She has also never cut this kids hair...he has long hair hanging halfway down his back...she says she wants him to be his own person and decide for himself how he wants his hair, not society... and he still talks baby talk and we have a hard time understanding him but I digress....)

Is there an age that is considered "late" for potty training? How do kids who are not guided by parents learn? What happens if he still hasn't learned next August when he is supposed to start Kindergarten?

I am certainly concerned about the potential socio-cognitive effects of this, but I don't know enough (as a new parent myself) about the technical details.

Advice?

eta...P.S...yes, I have read Brazelton v Rosemond articles....