My first real motorcycle was a 1970 Yamaha 90cc HT1B enduro. I was the second owner. At 14, I rode only in the dirt and on trails close enough to my house that it could be pushed to, as I was not allowed to ride it on the streets, even for a short distance. Not even side-saddle. Really, Mom, I promise.
Once I hit the dirt, however, I sometimes was gone all day. Kid heaven, it was.
I learned everything from that motorcycle, from how to fall down and not get hurt, how to climb a hill, how to cross a stream, how to land a jump to how to take care of a valuable (to me) machanical device. I learned how not to strip the heads of cheap Japanese phillips-head case screws and the ins and outs (sorry) of Heli-Coils. Tire changes? No problem. Waterproofing the airbox and tapping the cases to prevent vacuum-induced water fouling of the ignition? Figured it out all on my own. Chains and wheel bearings and suspension... all learned on this little Yamaha 90. Remembering how things came apart so they could be put back together just for the fun of it and much cleaner than when I started became a normal weekend for me. That little bike, more than any single other machine, taught me the bulk of what I know about mechanical devices, logical thinking and critical pathways.
When I sold it in order to purchase my Penton 175 (anyone remember those? KTM engine in a Penton chassis), it went to a... you guessed it, another 14 year old boy. He rode it, beat it, and then passed it on just like I did. Well, a few years ago I ran into the kid (now grown, naturally) and we began reminiscing about the old Yamaha 90. Turns out, it still exists, still runs and is still ridden by the grandchildren of the last fellow that bought it. We tracked the various owners over the years and as far as we can tell, it has had at least 17 (!) official owners. Mileage is unknown, as the speedometer was removed long ago in the interest of light weight and a 14 year old boy's desire to look more like the motocross heroes of the day.
And it still runs, 38 years later.