As others have said, forget what happened at 19. I ran a lot faster when I was a teenager, too. Sadly, aging sucks.
You are doing great! Dropping from a 9 minute mile to an 8 minute mile is huge. I wish I could drop a minute off my mile time.
The main thing now is to run more miles. Build up gradually to running 25 - 35 miles per week. I'd start by adding some 2.5 mile days, until you can do 2.5 miles most days. Then make your 2.5 mile days 3 mile days. You're not old, but you're not young, so increase your mileage slowly. I wouldn't worry about doing speed work or even tempo - do it if you feel like it, or skip if you don't want to. Just cover the miles one way or another. I would make sure you continue to run at least 5-6 days per week.
Once you've built up to around 30 miles per week, you can start following training programs. My personal favorite book is Faster Road Racing by Pfitzinger but there are plenty of options out there.
If you build up your mileage SLOWLY from your current 14 mpw to 30 mpw and keep being consistent, I guarantee you'll continue to see progress. Then start adding quality (ie speed / tempo) and long runs by following a training program, and you'll see more program. Just stick with it.