what ever age they are smart enough to know how to steer and use the gas and brake.. i'm working with a 5 yr old right now and having a blast.. we started out simple.. straight line in the yard stop and go with red and green plates.... and DAD hooked to the back of the kart with a tow rope just in case... Little motor, 79cc... biggest gear for the rear you can find (helps keep the kart slow) and a stop on the throttle so the peddle will only go so far... adjust as the intelligence of the driver grows. As for where to get a kart... someone on here will have one.. Good luck and enjoy the laughs..