For me, age 24, I'd see it extremely difficult to keep the same pace when I'm 50. Maybe I can do the same stuff, but slower.
So by then I wouldn't feel 'discriminated' if someone hires a more energetic, available candidate.
Or hopefully likely you'll do the same stuff, but smarter.
The amount of time and energy you put into something shouldn't be nearly as important as how much progress you make. Unfortunately, good metrics are hard, so some people and companies push for "activity" because you can roughly measure it.
In a job, I want to do one thing - to get as close as possible to defect-free, correctly operating code, on time and under budget. If you're not into that, I'll find someone who is.
Good metrics are impossible ( for now and for the forseeable - they may be congruent with the set of techniques for proving programs correct ) so it comes down to trust.
There is masochism in the world. I won't participate in your masochism if that's your thing.
A "hair shirt" is a garment ascetics wore for purposes of "mortification of the flesh." It's just masochism. It has unpleasant overtones.
An example is: everybody must chronically work 80 hours a week, as a sacrifice to the Tiki God, when the real solution is to sit down and figure out the best path forward.
It'd be fine if masochism were effective; I'd have nothing to say. It's just not. Fold the work better to get it done faster. There is always a way.
Some thing are just inherent Manhattan projects and will consume your life, at least for a while. These are much less likely than one might think.
You don't write the bugs you did at 24 - which means you don't have to stay up all night trying to find them. You don't produce the crummy designs you did at 24, which means that you don't have to spend two weeks fixing them. You know the library functions when you're 50, so you don't have to write your own code to do the same thing. And so on. You spend less time typing, but you still produce more value.
Personality might not vary much over time but careers, interests and aptitudes often change dramatically over decades.
I don't think you "keep the same pace". A lot of what I do now is, paradoxically, not doing things, until I'm internally ready to start work.