Your US Fed government (DOT) says that a "moped' must only go about 30 mph.
Anything faster is classified as a motorcycle.
However... a Yamaha Zuma is about the fastest 'scooter' you can buy... and it looks just like a scooter... but is classified as a motorcycle in most states.
And all states are a little different... and all police departments do not treat them equally...some would pull you over on a 38 mph Zuma and never even think it was a motorcycle (or care)... others might confiscate it and give you 3 or 4 tickets.
no drivers license
You might have to settle for a 32 mph moped like the rest of us and then hop it up a little if you really want to go 40mph.