EX: I have started to get up around 6am even if the room is dark and I am not getting enough sleep. I find it annoying, and nothing changed but my age.
I'm also not trying to generalize to everyone, I'm only surmising that there may be a lot of people like me. It's arrogant to assume your personal experiences apply to specific other people, but it's equally arrogant to assume you're a snowflake and that other people's experience is irrelevant to your situation. Everyone is their own unique blend of the many human commonalities.
In the modern era, there is no question that sleep hygiene is lacking for some, but it isn’t universally sleep hygiene, or universally scheduling, or universally a set amount of hours. It seems that we’re often dealing with different things for different people.
As I briefly mentioned in comment further up, the solution for me was a 9am wake up, and this seems to work consistently and easily with almost any amount of sleep. I can be just fine with 5 hours or 10. It just works. Prior to arriving at a career situation where I could set my own schedule, there were no combinations of solutions which allowed me to wake up at 6am and not be on autopilot and zombified for the first half of the day. And I tried just about every iteration and combination with diligence for years. Luckily I realized early enough in college to just never take classes before 10am or I would have almost certainly struggled.
If we can figure out ways to allow for flex schedules on positions which have no need for timing rigidity, I could easily see our collective productivity rising in measurable ways. And at the very least we won’t be needlessly forcing entire segments of the population to perform at half optimum levels for half of their days.
It really is a shame that so many in the world seemingly assume that we’re just not trying to sleep in the proper ways or that we’re not trying with enough conviction. Once I was lucky enough to be in a position where I could set my own schedule, my performance jumped significantly. I was no slouch prior to slightly altering my wake up time, but the changes after are remarkable.
Again, I am genuinely happy those changes worked for you, but for some of us, the same things just aren’t impactful in any meaningful way, sadly.
I can confidently say that multiple years of waking up early as a high school student did nothing to make me a morning person. 10-15 years later I find it more difficult to sleep in to 12-1pm when given the opportunity.
As a kid, I seem to remember my grandmother always waking up obscenely early. I feel like I've watched my mother transition from a "normal" morning person who will sleep in an hour or two extra on the weekend to waking up obscenely early consistently.
Matthew Walker alludes to this in his book on sleep; however, in his description it's not so much older vs younger people, it's just genetic differences that make some people sleep earlier and some later, with a fairly stable 60/40 or so distribution. Thus, the "dangerous" period (where everyone sleeps) gets reduced from 8 hours to, say, 3 hours.
Well, now you've introduced more variables into your anecdote. Any one of those could have been responsible for your feelings of 'well rested' and 'alert'...
But I recently spent the better part of five months going to bed at 9:30pm and waking up at 4:30am. Despite getting less sleep overall, I've never felt as well rested or alert throughout the day as I did during those five months and I've never had an easier time getting to sleep. The key, for me, was also modifying my eating schedule and screen usage (computer, phone, TV). I often wonder how many people who simply accept that they're naturally nite owls are using blue-light-emitting screens late into the night and eating their last meal of the day so late that their body isn't ready for sleep. Because I know that once I adjusted those aspects of my life, my sleep schedule magically responded.
The difficulty in maintaining that schedule has been societal pressures. Those five months were spent living outside of a city where noise, light and social norms around dinner time all make it very difficult to maintain while having any sort of social life. I'm still searching for a way to reconcile my sleep schedule with my intended lifestyle.