Delayed potty training in children can be a sign of autism because kids who have autism are harder to potty train than kids who do not have autism.
Still some kids just refuse to use the toilet and prefer to wear diapers and use the diapers like they have since birth.
If the child is not using the potty and showing signs of autism in other ways then taking the child to the doctor to get diagnosed with possible autism would be a good idea.
Some kids who have autism severely may not be able to ever use the toilet and may need to wear diapers for the rest of their lives.
But some kids who are just slightly autistic may eventually potty train by 5 or 8 years old.
I have a friend who has a kid who has autism and he finally potty trained at 8 years old so eventually they should get there.
Until he was 8 years old he wore diapers full time in the day and night and just one day a little after his 8th birthday he got the concept on how to use the toilet and decided he didn't want to wear diapers anymore.