At 9, my grandfather got the old Honda CT70 that my cousins had trashed and we rebuilt it. That is how I learned what tool is which and which side of the hammer to use with the correct words for a stuck part ;-)
I mowed my parents yard (4 acres) to earn money to pay for rebuild parts (Gramps only charged me for parts - who knows the hours he put in when I wasn't around?). This taught me 2 things. 1) Parts are expensive, so take care of your stuff and 2) Never buy a yard with 4 acres unless you plan to farm. It is just stupid to waste time mowing a lawn that size, so stupid that you will pay someone else to do it.
Anyhow, we got it together when I was 10 and he showed me the brakes first, then the throttle. After that and doing loops in the yard, we did clutch and I was off...when I turned 18 and was living on my own, I got my license and have been riding for 20 years now on the street.
Now my daughter is almost 8, rides in the steel sidecar with a much better helmet than the old Bell I had and my Mom gets nervous...