My rule is like the amusement park "you must be this tall for this ride". My passengers feet must reach the pegs. Even then, anyone under 18 usually only gets neighborhood rides. I couldn't handle being responsible for injuring a child. I'd rather be a known as a grouch.
For a few minutes, that 87 year old lady was a kid again. My mother-in-law was the same way when my husband took her for a ride.Not a kid, but the young lady of 87 years next door to me wanted a ride on a Harley for her birthday. She was never on a bike in her life, let alone a Harley......she loved it.