My first real ride was riding my shiny new bike home form the LBS. I had to stop and rest for five minutes halfway. I've measured since. It's 0.67 miles. So I was able to ride a whopping third of a mile (or half a kilometer) before needing a five-minute rest.

I've since moved closer to the LBS.

Five months after that first ride, I rode my first half-century. Okay, it was essentially five 10-mile rides strung together, but I did it.