I don't recall any reference to his autism in the anime it has been awhile since I watched first and second stage and I never finished the manga so it's possible I missed something.>>56044
That could explain somethings but not everything thinking about that realized another thing. The way Bunta treats him as his Dad is quite hands off but also gives him tasks to train his mind like he knows talking to him normally won't work. He also doesn't put pressure about him and school knowing from his autism he won't be able to work outside the family company.
Takumi is also referred to as special by older peers a lot.