Can you be 15 and ride a 50cc moped?

Apparently not in the UK, but if you hold a valid learners permit, you may operate a motor driven cycle with no passenger on non highway roads. The vehicle must reach the the speed limit of the roads, and if it doesnt, you must drive the vehicle on the right traffic lane. This law applies in the state of Massachusetts and many others, although, no, in the UK you must have a full license. For the state of Mass, once you have your license you may drive passengers in/on your motor driven cycle, in a side car or on the back, if there is a back seat.