I don't think anybody is suggesting there is some kind of moral imperative to train to the max - it's a sport, if it doesn't work for you, don't do it.
My experience is a bit different. Now 66-years-old and have competed consistently since age 14 or so.
In England, I ran for my area in high-school, then for the best part of 20 years competed as an English club runner, which unlike the U.S. meant a program of track and x-country leagues, as well as road-races. Not quite the intensity of U.S. College, as we all had jobs, but a lot of hard structured training. Did that for about 20 years - was fifth or sixth in the region at 3000m s/c at age 36, then moved to U.S. for work in late 30s.
Did a lot of club level road-racing over here, mostly 5k, then got into USATF Masters, and have pretty much trained in a very focused way for the last 25 years to the extent that I got into EIM (Easy Interval Method) a couple of years ago, and was doing four interval sessions a week coming into a championship meet.
Looking at things that others have mentioned here: when I was younger running provided the bulk of my social life. My friends tended to be from the running club, and in England at least we partied pretty hard on a Saturday when a meet was over.
When I came over to the U.S., initially not knowing anyone here, a running club again provided a social connection (and it helped that I was fortunate enough to relatively successful in local races). In fact it's where I met my wife.
I think, maybe, in England we were less body conscious, as far as worrying about being 'too skinny' to get dates. In addition, because of the club social environment at lot of the dating was 'runner with runner.'
The last 12 years or so, I've trained by myself. I think in that time I've run with another person about three times. I actually don't mind that as it gives me flexibility as far as doing a session at time that suits. I still do structured training and regular interval sessions. I did manage to win a race at the World Senior Games a couple of years ago (not as impressive as it sounds since it's 'World' in a similar sense to the 'World Series of Baseball - but fun none the less). I probably only race about four times a year, but they are all targeted for a big effort. I'm looking forward to setting some targets - God-willing - that I will go for when I turn 70.
I do enjoy the benefits of being fit (and I have now added weight training, which I probably should have started at least 10 years earlier), in things like being able to drop off a car for service six miles away and drop off. I don't think, however, without the carrot of competition I would have had the motivation to keep at it.
From a career point of view, I have been fortunate enough find a niche consultancy where for the last 30 years where I could work from home. I do work long hours, which I don't mind as it's been a life long fascination, but I also have the flexibility to train whenever I want. As with the running, I've no intention of retiring in the near future.
Of course there have been downsides. Like the OP and some others, certainly when young my whole identity would be caught up in running (I guess to a degree, I still tend to identify as a "runner" even though I'd be better known for my work). The other one that's tough to handle are injuries, and I have had a couple of knee surgeries.
Overall, however, I don't regret a lifetime of structured training and competitive running. It's taken me a lot of places I've never seen before; met a lot of interesting people; kept myself fit; and gained a lot of satisfaction from achieving competitive goals.