Seem to me that if you are old enough, your very first old bicycle could have been your very first bicycle, or second or third, etc... For most of us there wasn't a camera around back then taking photos of everything because film and processing cost money.
I'm only 34 and this is the case with me.
My first bike was a flea market bike, solid rubber tires with flat nobby treat, green plastic over frame to mimic a dirtbike if I remember correctly and a hard plastic white seat, loaf style. The better part of that memory was dad holding the back of the seat as I pedaled across the parking lot to the van and him letting go and I was riding for the first time without training wheels. This being the memory presents a loss indicating that there was already a training wheel bike on the scene... hmmm...
I remember dad buying me and my sister "matching" banana seat bikes, both in blue, but girls and boys frames respectively. Holley is 2 years older than me, but I beat her to no training wheels.
My first BMX style bike came next, and though it was a coaster brake bike, it had yellow mag wheels, yellow grips, and a yellow padded seat with the diamond quilted pattern. Silver frame and black handlebars with I believe checkered pads. I rode that bike till I got my first "beach cruiser."
Any one of these bikes brought up in photos on this forum would be recognized as an old bike, but it wasn't till last summer that I got my hands on a 1950 Columbia that got me building and riding again.