Oh my son was like that.
Late bloomer in the toileting department.
I didn't stress about it.
He also went to a Preschool at 4 years old, that accepted any level of pottying child. So that was no biggie.
But I knew, that by the time he went to Kindergarten, he would be fine.
And he was.
My son would also exclaim "ITS MY BODY!" or he'd get scared seeing his poop in the toilet.
Main thing, is that the whole ordeal does not cause the child to start withholding, their poop and not go at all. My daughter did that, even if we didn't push it. She just had stress and anxiety about it all. And she got constipated and we then... had to see a Pediatric Gastroenterologist, to remedy it. And it took, THREE months, for her to get over it.
By this point, per the specialist, it is a 2-fold problem: a medical problem and then an emotion based problem. Because, constipation, causes pain internally and when exiting. Hence, it affects the child. The specialist said.... let the child poop, even if that is in a diaper for now. And when they mature and are less afraid of the process, they will go in a toilet.
Constipation, once they start to withhold their poop, can be very serious and cause a host, of medical problems. ie: Encopresis, bulging bowels internally, hardness of poop, pain, blockages etc. Hence, I was very aware of this, with my 2nd child, my son.
And sure enough, he got it, on his own.