I agree that he could have additional needs (but the poster doesn't seem to be aware of it) but it could also be that his mother has taught him that it is quite normal for your parent to do this when you are 12 so he just isn't bothering to do it himself. If that is the case she is doing him a real disservice particularly if it means that he is "holding on" while at school as he could get constipated.
Being completely unaware of the social and cultural implications of your mum wiping your arse at secondary school, or being sufficiently distressed or anxious about wiping that it is more important to you than the shame of being wiped, is arguably quite good evidence of some sort of additional need, diagnosed or otherwise.
I think most girls with ASD go undiagnosed in childhood, personally. And average ages of diagnosis can mean kids at secondary. I don't know why some people seem zealously determined to pin it on inferior parenting, myself. "I think you are wrong". That's hardly a reasoned and cogent argument, is it?
I also think that, having one ASD child who was "you do it" from day one, and a toddler who has been "me do it" from day one, parents tend to assume that they are responsible for their children's behaviour at a far more basic level than I think is the case. You can shape, but you can't instil. Children come with their own instincts, needs and wishes, as the poster who was unable to allow her parents even to apply her sunscreen from a very early age can show.
I just find it a bit odd, the determination of some parents to prove other parents inferior. My son will always be inferior at bum wiping to most of his peers. He will always be superior in natural kindness and innate intelligence to most of his peers. That being the case, the bum wiping seems pretty trivial, really.