Masturbation is not entirely uncommon even at that age and it isn’t necessarily something to be overly concerned about. As with typically developing children, as your son gets older, expect him experiment as he becomes more familiar with the sensations he is experiencing. Usually, the focus for children with
autismAutism
Autism - resources who begin masturbating isn’t on getting them to stop but rather teaching them when and where it is and isn’t appropriate. It sounds like you are worried that this might be related to possible
sexualCauses of sexual dysfunction
Erection problems
Female sexual dysfunction
Sexual problems overview abuseAlcoholism
Chemical dependence - resources
Child abuse - physical
Child abuse - sexual
Child neglect and psychological abuse
Drug abuse
Drug abuse and dependence
Drug abuse first aid
Family troubles - resources
Laxative overdose
Signs of drug abuse or some sort of sexual encounter that he might have had. The masturbation, in and of itself, is not atypical and doesn’t necessarily indicate this. If you have concerns, keep your eyes open for any other signs and talk to his teachers about what they are seeing but, if it is just the masturbation, it does not need to be a major concern.