for the first 30 years behind monitor (and that is if you start with perfect eyesight).

It is really hard to understand/fell issues of the others until you hit the same issues yourself. This is why there are accessibility and good (not pretty/cute/beautiful/etc.) design guidelines which one has to follow even if the one doesn't see the need for it. ~15 years ago i noticed when some of my older colleagues started to use eyedrops, to mention eye fatigue, etc. while i was easily doing 12 hours almost non-stop, and i was pretty dismissive about their "minor" issues. Well, these days, closing on 50, i understand much better what they were talking about back then :)

And for those healthy&happy youngsters who may want to walk a mile in someone else's shoes or just read a light gray text with white background :) - aging/disability simulation GERT suit:

https://diamedicalusa.com/medical-equipment/manikins/wearabl...

"The age simulation suit GERT offers the opportunity to experience the impairments of older persons even for younger people. The age-related impairments are: opacity of the eye lens, narrowing of the visual field, high-frequency hearing loss, head mobility restrictions, joint stiffness, loss of strength, reduced grip ability and reduced coordination skills."

is a terrible standard for main content. You should be able to read it for the all.

You can read it, but many people do not have high-performance monitor and high-performance eyes.

Users can configure monitor/browser defaults for contrast and text however they like; web devs shouldn't try to forcibly reduce constrast for the primary content that is supposed to be the main recipient of visual attention.