Returning to running after 2 years- time to sub 17 5k

I'd say a year, plus or minus 6 months.

I'd start out with less milage. I did the same thing as you. "25 miles is nothing." My ankles still hur, 3 months later, from starting with too much milage. If you are wanting to start training in a few weeks, start now instead. Do a month with low milage. Slow, easy miles. Don't let your ego get in the way. Don't push the pace at all for at least a month. Your lungs and muscles will feel great but your connective tissue takes much longer and you won't know it's progress until it starts hurting.

I took about 8 months off with little to no running when I was 22-24. Prior to that I was a 4:05 1500m and 15:30 5000m on the track.

In July I started training and my the end of the month ran 19:36 for a 5000m track race at a local all-comers race.

4 months later went 26:30 8k for a road race.

I'd say 4-8 months is a good estimate.

I am in the exact same situation as you (just a few years older). I am thirty. 17:03 5k 13 years ago. I built up to ~70 mpw over about six months and ran a 1:25 half marathon. That was 2.5 years ago. I injured myself just before it and ran anyways. Limped around for weeks and stopped running completely until a few weeks ago.

I am trying my best to start very slowly. I was thinking of taking pretty much the rest of the calendar year before trying to go beyond 15-20 mpw, but I had let myself go (gained 20 pounds, etc.). That looks more and more conservative each time I go run. My only real advice is be brutally honest with yourself about how you are feeling during the first month or two. That is where I am trying to keep my head at. I probably would have been well served to have done the same a few years ago. Best of luck.