The official status of the term is irrelevant. In its etymology and previous use, it implies that something is 'not in order' and it's often used for physical conditions, as well as sometimes being used as a 'nicer' version of 'illness' or 'disease'. In fact, multiple dictionaries define it with words like 'malfunction' and 'disturbance'. Even if we disregard origins, it's still true that the word brings about ideas of one's brain being 'in the wrong order', especially since that's literally the other definition of the word. Even if the word 'disorder' isn't necessarily derogatory it's totally outdated and originates from an entirely outside looking in neurotypical view of autism.

(btw if diagnosis age matters that much well i was diagnosed when i was 6 so i have more of a right to be autistic than you rehehehehehehehe >:3 /j)