First did it as a freshman in HS back in 1994. 4:56 early in my first season of indoor track after one season of XC. Was doing maybe 20-25 miles per week. Ran my last competitive race in 2009 (mid 2:30s marathon), but maintained the ability to break 5 until 2014 just off maybe 15 miles per week of easy running and 30 minutes a day of bike commuting. After that kids kept me from training even that much and I didn't even attempt it for a couple years. Currently trying to get back to the point where I can both break 5 for the mile (currently in the 5:05 range) and 3 hours for the marathon (ran 3:05ish in the spring) before I turn 40.