How old do you have to be to ride a mini chopper on neighborhood streets?
A mini chopper is not quite small and light enough to be considered a moped/light scooter, so I believe you have to have a license to drive it on roads. In North Carolina, in order to drive a 2-wheeled vehicle without a license, you have to be 16, wearing a DOT approved helmet, and the bike has to meet these requirements:
50cc's or less
no external gearshift device
30 mph maximum speed
209 lbs or less
wheels have to be 10in in diameter or more
Many states will vary in their laws, but look up moped/scooter laws for your state and if your bike qualifies, then have fun, and be safe.