my 53 yr old dad rides our little 110cc along with my cousins in their 20's when they visit. sure they look funny but at the moment its the only bike we have. travis pastrana who is a pro is 6'2 and rides a 125cc at xgames. it seems to fit him. but then again he is a pro. i would go anywhere from a 125cc to a 250cc. go to a local dealer and sit on some bikes to get a size feel. i would go with a 4-stroke being a beginner. also dont fall for the $500 bike online. they are "chinese brand" bikes and are cheap becasue they are cheaply made and because they are cheaply made they are unpopular and have more problems. and due to low popularity new parts are hard to find. stick with yamaha, suzuki, kawisaki, and honda.