I don't think it's the employer's responsibility to tailor the job to match a candidate's chosen lifestyle, or that not doing so means you're discriminating. I think people need to be responsible for their own decisions, and if that means you're less competitive relative to another candidate, that is not the employer or the other candidate's fault.
Offering below-market salaries for 80 hour work weeks isn't illegal age discrimination even if this highly correlates with age, those are legitimate criteria that affect work performance, and thus are valid; just as criteria that require workers to be able to lift a certain weight is a legitimate criteria if appropriate to that job role, even if it would disqualify almost all women for applying.
Disqualifying an old man because you think that people of his age won't work 80 hour weeks for a poor wage or can't carry the required goods is prejudice and illegal discrimination. However, disqualifying an old man because you know that this particular man won't work 80 hour weeks for a poor wage and can't carry the required goods is fair game, it's a reasonable evaluation of a potential employee.
Systemic bias exists. One manifestation of that in this industry is the signaling in certain job descriptions and hiring practices. We needn't point to explicit, specific examples (e.g. "hiring manager told me point-blank 'sorry, we do not hire people over 30'") to see a broader effect.
You don't seem to understand how discrimination works: the advertisement you describe discriminates against older workers because of how lives typically evolve with age (e.g. ability to sustain long hours, family or other obligations, etc.). The two scenarios you describe aren't objectively independent or even clearly separable.