Our 3yo DS has a number of behaviours that have had us wondering about ADD. Without us having mentioned it, his nursery class teacher also bought it up and has arranged for an EdPsych to come in and observe him for an afternoon. He's our only child so we don't have much to go on in terms of what is normal (or as normal as 3yo's get ) and what isn't. If anyone's been through the process already and wishes they'd asked/mentioned something at the time I'd love to know.
Where I live, they won't diagnose ADHD until the dc is quite a bit older, as so much of what might be seen as ADHD in a 6 yr old, is very much within the range of normal toddler behaviour, tbh.
I would also have a think about what difference it would make at the moment, if he did get a diagnosis - if it's strategies to help him cope, then surely you / The Nursery can start putting them in place anyway? If he doesn't get a diagnosis, but struggles with his hyperactivity / boisterous nature, then I'd think more about how I can use up some of that energy at this age, and think about techniques to cope with 'flashpoints' in his day.