I thought I was done when I started my career in my late 20s. I was still running for fitness but not really training as the 60-80 hour weeks were taking a toll. I'd do a race or two a year. Finally after 5 years of this, I felt kind of embarrassed at my race times, I couldn't even run 6 min pace for a 5k anymore. I started training again full bore and racing and moved to a new position with only 50 hours of work a week on average (with very uneven overtime, could work 40, could work 80). I basically lost a year to the pandemic as I lost the track I train on (and no other is available to me), had no races, and was expected to pick up the slack for teleworking coworkers. Finally, I'm getting back to where I was just before the pandemic at 34, 20 years after I started competitive running. I'm hoping to be in shape to pr in another couple years, with luck sooner.
I guess my long winded response is to say you never really know when its time to quit. I for see myself chasing masters times and trying to lose as little as possible in my 40s, 50s, and beyond.
I totally get why guys who were subelite or even just good in D1 hang them up though. I was just some D2 also ran and always have felt there is more I can achieve and better training that I can do to get there.