Living Dolls

Tyler Cowen thinks "the Ashley treatment" is scary. I agree, although not because I think it's particularly damaging in this case. Ashley, the "pillow angel" who has been treated so she will be child-sized forever, has and will always have the mentality of a three-month-old. But couldn't most of the same rationalizations for this be applied to less profoundly mentally disabled people: those with the mentality of one-year-olds? three-year-olds? nine-year-olds? In every case, growing to adult size makes it more difficult for their caregivers; in every case, puberty is likely to bring both physical discomfort and emotional difficulties (none of these hypothetical persons could consent to sex, but they are likely either to be taken advantage of or to engage in inappropriate behavior toward others based on hormonal urges they will never understand). At what mental age could we say that something like this is wrong?