Regarding "some people are naturally better..."; it took me ~4 months, "running" 4 days a week, to be able to jog a 3 mile (~5K) run in ~30 minutes. My age then was 28.
My friend, who never worked out in any way, woke up with a hang-over and decided to join some friends for a competitive, cross-country 10K... he came in first. He was 22 years old, IIRC. His father is a dedicated marathon runner (qualifies for Boston Marathon), so that partly explains it.