I reckon I'm in pretty good shape, and I feel great after a 3-5 mile run. I suppose if I had more time to train I could work my way up, but I don't. And, to be honest, I would probably rather spend that time in a BodyPump class or watching F.R.I.E.N.D.S. with a big bowl of berries and some dark chocolate.
Moreover, I don't think that you have to run miles in the double digits to call yourself a "runner". 3 miles a few times a week is more than enough justification to buy those cool shoes you wanted or to tell your friends about the run you went on that felt so amazing. And you know what else? Even a slow, short jog has infinite benefits for your heart health and overall metabolism. Just do something.