X has a micro with a seat which we gave him for Christmas and he is just about starting to get the idea of pushing it along although I have to leave at least 45 minutes for the 0.25 mile to school if I want to get him scooting on it! We haven't really tried him on a standing scooter - the girls have 2-wheelers which he does keep trying but it's not going so well!
One of my friends has just started bringing her ds2 on the school run with a scooter and he was 2 in November but is pretty steady on it now.
We gave e her scooter for her 2nd birthday, I think, but it wasn't really until the following summer (2.75ish) that she could actually really get anywhere on it, although she started doing the school run on it when m started school so she would only have been just 3.