Weighing in with the oldest (so far) Yamaha is...me.
It's my 1979 Yamaha XS650F. She's my first street-bike; I bought her in 1993 for $400 from a friend of the family, when she decided to sell her late husband's bike -- with the caveat that it didn't run, and would I like to look at it? Turned out all I needed to do was clean the sparkplugs, put in clean gas and kick it a few times and it started right up. Her husband was the original owner, and had only put 6400 miles on the bike before passing away. she asked, "I was going to put it in the paper for $500, but would you want it for $400?" -- You bet your sweet baboo I do! In the last 14 years, I've run the miles up to nearly 20,000. That picture is the only one I have on the web right now...taken some time in 2000.
So, I rode my new bike home and commenced to riding the wheels off it. I crashed it the first summer I owned it, I rebuilt it, I got back on it, and re-commenced to riding the wheels off it. I took it to college with me, and when the campus police started harassing me about parking it under my apartment's balcony....well, I just moved it into my living room. That Christmas (Christmas '94) I strung lights on the bike and put presents under it.
I'm a computer technician by trade -- a nerd if you will -- and a father of four. I'll celebrate my 10th wedding anniversary this August, and yes, I said FOUR kids... my 6yo boy, 4yo girl, and 4month old twin girls. And yet, I've still managed to hang onto my bike. I see ads in the paper and on eBay "Having baby, must sell bike," and I say *cough*bull$#it*cough* My XS has been with me the whole time, from living at home when I bought her, to college, to Indiana where my then-girlfriend (now wife) and I spent 5 years, and back to Michigan where we are now. I've only had her on the road about half the years I've owned her, but I make sure she runs every year. I'm hoping that this year is another "on the road" year.
I've been riding since I was 15 -- my first bike was a 1971 Honda SL125 dual-purpose, and I fell off it in the woods a whole lot on my way to learning bike control and stuff.

When I got my driver's license I took a motorcycle safety course and got my cycle endorsement, so I could ride my little 125 on the road at 50mph, flat out. Quite frankly, I've been hooked ever since. Every time I ride, I want to tell other motorcyclists "Shhhhh!!! If we tell too many people how much fun this is, someone'll get jealous and it'll be banned!" How has Congress missed this? Heck, I don't care, as long as I can keep riding.
Maybe I'll find the picture of the "Christmas Bike" somewhere in a box...