For the record, as I near 40 years of age, I can't run a 20:00 5K. And I used to be able to run a 16:00 5K, 15 years ago, and I still run ~20 miles a week and play tennis 2-3 times per week (and can outlast most anyone on the court from a cardio perspective).
To run 16:00, I had to train just like the link indicates. 50+ mile training weeks for several years with lots of "strength" running as well. It was hard (at least it was for me).
7-minute pace would be a good goal for me these days.