I've said before - my internal alarms started going off with my oldest when he was 2 or 3, just with inability to follow simple instructions on his own and secondarily with impulsive behavior, frequently in contrast to instructions given immediately prior to his action.
Everyone from his day care teachers to his grandmother said 'it's just a boy acting 2 - 3 - 4- 5- 6...'
When he got to elementary school it was like WHOAH. It was pretty clear he was far more disruptive (not in a naughty way, just in a can't-help-it kinda way) in class; I was appalled the first time I went to observe. And he would get in trouble for stupid stuff - bad reactions to situations exacerbated by his limited ability to read between the lines in people's behavior; doing something against the rules that a friend told him to do (but wasn't dumb enough to get caught doing).
When we got him evaluated end of 1st grade, no surprises.
The behavior certainly continues, and he benefits from a lot of the same tricks Tiggerific talked about - no meds, but behavior mod therapy, list making, talk therapy with a psychologist (though I've been bad about scheduling this recently), physical activity has helped a lot, and an IEP in school with roving support staff and extra 'advisory' class (study hall for most kids, but for him it' s make-sure-you-have-your-shit-together) time.