Davey's legs wrote:
But you do need to put the miles in AND probably have an aerobic system (a.k.a. choosing the right parents) which helps you out.
The aerobic system is HIGHLY trainable. You can go from sedentary / not able to run more than 2 min to a 16 min 5k if you start training without much talent (at young age and normal 19-23 BMI). Speed on the other hand is highly genetic, but it's not that important for distance events.
Stop blaming genetics for hobby joggers. I'm tired of hearing all the time I got talent just because I improved from 21 min 5k to 17 min in one year at >30. It's just hard, solid work week after week and smart, consistent training. And 17 min is still fucking slow, most hobby joggers got a complete misunderstanding of what's fast and what not.
Talent matters at the highest level - it ultimately decides who gets the medals at Olympics, but hobby joggers should never use it as an excuse for their times when they haven't even optimized training and everything around it yet or are doing 30 mpw and think that's a lot.
Also to the poster before, 18 min for a 50 year old is extremely far away from world-class (it's a very good time for that age, sure but world-class would be 15-16 min).