I guess it depends on mindset and your personal goals. I ride for fun, stress release, and exercise. I've never been an athlete, never played team sports, and so I don't have that "competitive" drive. I don't go out to "train". My rides are my training. I could stand to lose 20lbs and I don't have a beach body, but I also don't care any more. I DO take satisfaction when I finish a ride and found I've set a PR on strava, or I'm say, #14 out of 400 for a particular segment, especially when athletic 20 somethings are setting the bar.
But that doesn't drive me.
I have a fun, and steep, 2+ mile downhill near my home, which I start out most of my rides going down. It's almost 600 ft. of elevation drop. It's like riding a roller coaster. I started trying to constantly get a PR on it. But it requires maintaining +25-30 mph going down and a peak of around 40 MPH. I started questioning why I was doing this. What was the purpose to set a personal record? I just don't need a crash at 40 MPH. I reached my limit.

As far as how hard to push, I'm 56, almost 57 and as mentioned above, I listen to my body and let it dictate how hard I push. Some days, the energy just isn't there. Some days I can climb the mtn back up to my house and feel like a million bucks, other days I have to stop and take a rest going up. Some days 50 miles is easy, other days 30 is difficult.
As I mentioned, I don't have many goals beyond fun and exercise with the added benefit of stress relief and better health.