My PR is 22:50 and I am 50 yo. Been running steady for 3 years. I would like to get to 22 or 21:30. I run alot of races, at least 2 per month. that is what I consider my speed work. How much lower do you think I can get that time down?

With only 3 years of running under your belt, I would wager that you can go lower. How much mileage have you been doing over the 3 years? Are you willing to run more?

i have been averaging 20-25 mpw. i could probably get to 30-35 but that is about it. it is taking me longer to recover after long runs. i have to take at least 1 sometimes 2 days off after a long run (10+ miles)

I notice that your long runs of 10+ miles appear to be about half of your total weekly mileage. You might be better off to spread your mileage a little more evenly over the week. This way your long run will be a few miles shorter and not take so much out of you. This should allow you to increase your overall volume. Also, what is your reasoning behind not being able to run more than 30 - 35 miles per week? I think if you build your mileage base slowly enough, your body will adapt to the increase workload. And if your goal is race times, I think that a sustained increase in mileage would be most certain approach to accomplish this.

I've seen a 50-year old run 17-flat. So I'd say that's about as low as you can get.

I also noticed this guy Pete Mcgill who has a running blog dedicated to Younger Legs for older Runners. Not quite 50 at 47, but he posted a blazing fast 14:49 for the 5K this year.