Been there. You want embarrassingly few miles?
When I restarted in March of 2006, I rode my brand new "old man hybrid bike" home from the LBS. I had to stop halfway to rest. Total distance? 0.65 miles. A little more than half a mile, and I had to stop and rest halfway through that.
It was weeks before I could ride the two miles to work without stopping to rest. But, perseverance pays off. I did my first 50-miler that August and my first metric (100 km, 62.125 mi) that October. Even though I did them in ten-mile increments between rest stops, I did them.
It's dead flat around here, so even expressway overpasses gave me trouble through the following year. I didn't get good at hills until 2008. Twenty-eight months to the day after I first turned a pedal, (and two bikes later) I rode to the top of the highest paved road in North America, Mt. Evans, just west of Denver, CO.
Give it time, and keep turning those pedals.