An autistic child can be harder to potty train and get out of diapers than a child who is not autistic.
However most children who are autistic are able to be potty trained and stop wearing diapers by age 3 to 5 years old.
I knew of a child I used to babysit who was autistic and he was not potty trained until age 9 years old so I had to change the 8 and 9 year old boys diapers.
I didn't mind it and I just let him decide and took it slow.
His parents didn't want to force the issue and I figured he would eventually get it.
He wore diapers full time until a few months after his 9th birthday.
Most normal children are potty trained by age 18 months to 2 years old and some children continue wearing diapers full time until near 4 years old and that is normal as well.