how old do children have to be to screened for ADHD?

Hi there. I think that he is a bit young to be diagnosed with ADHD. You haven't given much info on what is happening, but at his age, he is probably being just the normal nearly 2 year old. They call it the naughty 2's. If you are really worried have a word with your doctor next time you take him to see him/her, but I think that at his age he is far too young to be diagnosed. Probably around 5/6 years onwards, but I really could not say because it actually depends on the child. For the moment, try not to worry too much, just put it down to the "naught 2's"for now and see what happens in later years. He might just be playing up to get attention, but try to be patient and see how things go. Good luck!!