There have been some documented cases of adolescents on the autism spectrum experiencing brief hallucinations and delusions. So it is possible, howevet the hallucinations you describe your chatacter having are specific to schizophrenia: hearing clear voices multiple times telling the person to do things, seeing the same things over and over. So if the character needs to have these types pf hallucinations as part of the plot, the character could always have a form of autism AND early-onset schizophrenia. Some studies even claim evidence that schizophrenia is way more often developed in brains that are on the autism spectrum... not really proven yet. Its quite possible for a person to be both though.
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Seeing beyond the 3rd Dimension.