Sometime in my late 20s after learning enough about health in general I realized that sleep was much more important than most believed and I decided my routine was unhealthy. I dealt with it with similar methods mentioned on other comments. No caffeine in the afternoon, blackout curtains, red lights, limit light when it's dark out, not eating late.
That was about seven years ago, I'm now 35 and I'm not a night owl anymore. Part of it is probably getting older, I've heard that this frequently happens to people as they age. But I noticed the changes within a few months of taking sleep hygiene seriously. A few years ago I threw out my alarm clock because I hadn't set it in a few years (I'm lucky that I really only have to be at work by 10am for a standup so it wouldn't matter if I overslept). I can't remember the last time I woke up later than 7:30am, that's late for me now. Usually it's around 6:30am. I am wide awake when I open my eyes. My main sleep problem now is waking up too early and not being able to fall back asleep. I'll then get tired and go to bed early, and wake up even earlier the next day.
I feel better than I have at any point in my life previously. It's certainly possible that many people here with sleep problems have naturally different rhythms. It's also possible that certain obese people are naturally obese and no amount of diet or exercise changes will fix it. I have personally come to the belief that having a sleep cycle which is not mostly aligned with the natural patterns is unhealthy, regardless of whether it's "natural" or not.
If anyone is interested in specific techniques I have all sorts of little hacks, although I don't have to use many of them anymore.