I have a friend that ran a 5:30 mile in middle school with no training.
I have another friends that does not really run (and when he does its like 3 miles at 9:00 pace), yet he runs 19:00-19:30 5ks no problem.
It took me a year to break 20 in the 5k and 5:30 in the mile with consistent training. In middle school with no training I barely broke 8. I got in really good shape and then got hurt and took a month off (very little cross training), and when I came back I had added like 2:30 to my 5k time and it took me like 3 months to get back into shape.
Is there anything I can do to improve my "base fitness" or did I get screwed genetically?