I am a 22 year old male and have been running for 4 years. my first ever 5k was 32 and my first mile was 9:50.
Since then I have revamped my lifestyle and currently this is my life:
Two workouts a week (400/800/hill repeats or TT)
A long an: short tempo run alternating weeks
One long run every ten days
A tonne of cross training on the bike and hiking, also occasional freerunning (we call it that here in the auk insteadf parkour as I'm aware this is a mostly ametican site)
50 miles per week at easy/moderate pace (75% easy/25% moderate)
BMI of 20 so weight isn't the issue
Bloods = good
Nutrition = good
Sleep = good
I don't drink and I don't smoke.
My 5ks are currently in the 20:30-22 range and have only ever hit sub 20 three times. I literally look at the sub 18 guys like they're gods but most guys my age who run claim that anybody can do that and talent doesn't really come in until about 16:30...
I struggle to break 20, I worked with a coach who ran in high school all last year who managed to bring me down from 22:45 to 19:50 but I can no longer afford it so I'mon my own.
These days, I can't even come close to sub 20 even though I upped my milage this year from 35 to 50. And I know most people here would say 50 is still low milage but I'm talking about getting in 19:30 shape here, not 15:30.