It is usual protocol to wait until the earliest age of 6 before diagnosing for adhd
because all kids
before that age show so much variability in behavior. Many kids
prior to 6 will be impulsive, hard to settle down, on the move, have no filter, talk in loud voices and move from thing to thing quickly without finishing something.
I believe you could google adhd and find a listing of symptoms. It involves the nervous system and people will sometimes call these kids hyper.