Can I break 3:10 in September?

I'd say there's a strong possibility you can break 3:10 if: your training stays consistent; you continue to progress; you get good weather on race day; and you pace yourself during the marathon. Eire is a great course if the weather plays nice.

Based on the equivalency calculator I like, your 32:30 5-miler is equivalent to a 3:09 marathon. Your recent 19:36 5k time in less ideal conditions is also indicative of 3:09 without adjusting for the weather. Of course, equivalency calculators assume your as well trained and mentally prepared so they should be taken with a grain of salt. And since you've run a sub-3 you know how much nutrition, hydration, and race day conditions can impact a marathon. With 11 weeks until race day it's likely your 3:20 BQ will be easily achievable by simply maintaining 40-45 mpw with nothing more than a moderate amount of marathon pace miles in a weekly long run with a build to 2 or 3 long runs of only 18-20 miles and no threshold/interval work (if you go out at 7:35/mile and don't think about picking up the pace until after say 15). If instead you start something like Pfitz's 12/55 plan (skipping week 1) now and I'd give you the following odds assuming typical Erie weather and no setbacks: sub-3:20 95%, sub-3:15 80%, sub-3:10 60%, sub-3:05 30%, sub-3:00 5%.

Good info, thanks. I've been following my own plan for the most part, but just mileage and I select the pace based on the weather and how I'm feeling. I've done the Pfitz 18/55 in prior races, but never really followed it properly, especially the workout days. I'm much more consistent than my old days, but older and slower.

What do you consider moderate amount of marathon pace miles? Prior to today, I've only managed maybe 30-35 miles sub 7:14 pace, including the races. Partly because I was still building my base and now because the dew points are low to mid 70s on all my runs. Today was a pretty hard effort for MP minus 20 seconds. I rarely get sub 7:14 pace during my long runs, maybe at the end if I get out before the sun and feeling good at the end of my workouts.

I'm hoping my fitness keeps improving even if I'm running 7:30-7:40s at the end of my long runs, but it's 85 degrees and humid.

I get it - I'm older and more prone to injury as well. You and I are in the same BQ age group based on your 3:20 BQ. Based on your 5-miler I think you can be very conservative and get to 3:20. By moderate I had in mind perhaps 5 miles at MP, building to 10-12 miles at MP 2-3 weeks out. With those brutal dew points the pace for the MP miles should be adjusted to account for the conditions. If you can, run them by perceived effort. I'm in Virginia so the weather is brutal now too. I'm running about 25-40 seconds per mile slower than I was in April because of it. And you probably won't give up much by running them at an effort 10-20 seconds slower than what feels like MP effort, though by the last 3-4 weeks it'll be better to ratchet them down to MP effort. And as an alternative you could do something like run MP miles during a mid-week run on even weeks and during the long run on odd weeks. Just keep in mind that if it's in the 50s in Erie on race day you'll be way faster than during summer training in Florida.