You look about 20 years old to me -- not like a kid -- but I have found I'm not a great judge of age. I thought a 60 year old co-worker looked 40, and thought a burly bearded 19 year old co-worker looked 35. I think it's a common feature among autistics that we often have difficulty discerning the age of other people.
My advice is to not let your "appearance age" bother you too much. One day, you might enjoy the thought of looking younger than you really are, unless it's limiting your career options or your ability to find a romantic relationship.
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DSM-5 Diagnosis: Autism Spectrum Disorder, Without accompanying intellectual or language impairment, Level 1.