I'm a 38yo male, about 175 pounds, with no running experience in school or college. So I started running at 27-28 yo, and did nothing but 10-11 minute miles. I had no GPS watch and no awareness of my mpm, I was just trying to get my dog some exercise. So about 2 years later (I then weighed ~200 lbs) I decided to sign up for a marathon (6 months away) and in a month I ran my first 5K (22:42).
A year later, I will assume because of the base I built up in training for the marathon, I was running 20:30 5k times. Signed up for another marathon, built the base, and a year later was running 19:30 5k times (32 yrs old), where I'm still stuck to this day at 38 yrs old. I ran 3 more marathons, 1 a year after this, with my longer distance races still improving, but my 5k times still stuck, and mile times getting slower.
So, I was in the same boat as you 8 years ago. I recommend you just run more miles for 2-3 years, building your base up, before you add in any speed work (i.e., intervals).
What does a typical week of training look like for you?
I also like the post above about the mental aspect - great post.