2018 was my first year of commuting by bike. I actually started Sept. '17 and carpooled from Feb-July '18, so the end of 2018 was about 10 months total. I didn't consistently track mileage - I was undecided between Map my Ride, Strava, a cyclocomputer, and no tracking. I eventually settled on tracking w/ Strava. I estimate about 4,000 miles total for 2018. If I ride continuously for 2019 I expect to have about 6,000 commuting miles plus whatever joyriding I do.

I knew a 25 mile round trip daily would be a lot, but I since I'd never ridden that much prior to commuting I didn't know what to expect as far as the sort of effect it would have on me physically and mentally. I used 3 different bikes, (2) vintage roadies and a hybrid drop bar conversion. I got hit by a car in August and reevaluated my commute. I decided to slow down, decided that 15 mph was good enough for commuting. I still stand by that decision but if I have a tailwind or am feeling spunky I'll push it a little. I'm pretty often surprised by the small things that over time make a cumulative difference, like adding a rack and loaded pannier. Didn't seem like much at first, but after a few weeks definitely started to feel the weight, but even more the wind resistance of it. Or 1/8" of saddle adjustment, up or down, forward or back. Doesn't seem like a big difference at first again but after a few weeks ... so at the very least I've learned to wait a few weeks before I've settled on any change I've made.
I think anybody who is commuting much over 10 miles total every day is doing a lot. And I think any one way commute over about 6-7 miles is quite a bit. I'd rather commute less and joyride more, but I'm not about to provoke a job change to do it.
FWIW I AM about 15 lbs lighter than when I started, and I AM probably in the best shape of my adult life at 37, but I'm so tired most of the time that I don't even think about/realize it. That has less to do with the miles and more to do with what I do off the bike.