It depends on if the person has had riding experience and what type of motorcycle the prefer. 250cc top speed is about 95 there very efficient. There's 600cc that's alot faster it will get up and go but only if you tell it to the power is easy to control. Then there's 1000 that's a heavier bike with alot more power and is for an experienced rider but it's not uncommon for people to get them as there first bike. It all depends on what you're into do some research look at all different types of bikes. My first bike was a Kawasaki ninja 600 zx6r that was a fun bike.
250cc is about it. They are small and light, so you must be very careful. I had two or three 350cc - 400cc and all were good on the freeway, I even went on a 800 mile round trip once or twice, no problems. Be advised you will face 60_70 MPH winds - really hard on you (buffeting) unless you have a good suit and helmet.