What kind of question is that? Did you think you learned something that makes you an adult? What was the exam?
Well it is actually somewhat of a valid question legally. One of the main legal distinctions between adult and child is the ability to accept legal responsibility and sign contracts. At least in Canada those with severe disabilities can sometimes be found to not have the capacity to be considered a legal “adult”.
That doesn’t make people a child. It just splits people into adults that cannot accept legal responsibility and adults that can.