Probably 16 years old or have a drivers liscense. and im pretty sure you wont find a dirtbike for less than $1500, probably atleast $1900 or so just for a decent one, but if you get one, get a honda or a yamaha, because they are built well and a yamaha is better for beginners, also if you absolutely dont like clutch or you can never learn how then get an automatic, they are easier to work with and everything, i have a 1988 yamaha blaster 200 4-wheeler, which is great for beginners but im over the thing, i maxed it out already but thats just a 4-wheeler, dirtbikes differ greatly from them. and im not sure that you can get a street legal dirtbike unless you do some heavy modifications to it to make it legal according to your state, i think for michigan you need turning signals, a max speed of atleast 45mph, side view mirrors, a breaking distance of at the most 55 feet or so going at 30 mph, head lights/tail lights and that other stuff. so you could just get a normal dirtbike and look on the net for what you need to do to make it legal.