I must be doing something really wrong, i'm 41 run 50km a week (for 10+yrs) and my <Z2 is 8:52min/mile. Best i can do is 5km @ 7:15 and i'll be dead running 19

I must be doing something really wrong, i'm 41 run 50km a week (for 10+yrs) and my <Z2 is 8:52min/mile. Best i can do is 5km @ 7:15 and i'll be dead running 190bpm+ for the whole duration (and sometimes 200) must be the genetics.