A good amount of the components can be put together by a 3yr old but not all. The same can be said for pulling them apart once you have built something. Maybe more suited to 4+ but at least as an adult you get the first year building the different automobiles yourself :D
Tip: Some of the smaller parts get stuck together, green ones and white ones. Just pop them in a cup of boiling water for 20 seconds or so and then fish them out. They should then come apart with a little twisting motion.