My father, but I was 15 at the time and as he was a rider himself I was quite pleased he had confidence in me, especially as I had just passed my test for a full licence.
My youngest, probably one of my sons at about 6 years of age. You have to be careful with kids on their capability of holding on. I don't think I would carry anyone younger than that, and I would also watch my speed. I think it would be important that they could rest their feet on the pegs.
Having said that I was carried on my father's bike sitting in front of him on the tank at around 2 years of age, but those were non PC days and it committed me to a life-time of motorcycling.
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Ride on !
