He is autistic, and a screencap of his diagnosis shows:
Lower Spectrum Autism; Query Aspergers Syndrome? Complicating Factors; Odsessive (sic) compulsive disorder, Acute Hyperactivity, Night Terrors; Query Bi-polar di-order (sic).
Handwritten notes, and the general depiction of the mental health services in the program suggest that this diagnosis may not be completely accurate though. AS looks like the right guess though, and its quite a good portrayal, and a little less stereotyped than the usual. (Though I query that anyone "obsessed" with model planes would be buying the bod airfix kits at that age.. surely the posh Italieri ones with the after-market brass-etched parts....)
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"There is a time when the operation of the machine becomes so odious, makes you so sick at heart,
that you can't take part" [Mario Savo, 1964]