People's circadian rhythms change over the course of a lifetime very considerably. Trying to keep all age groups on the same schedule is actually a pretty bad idea. Check out the book Why We Sleep. I think especially how we treat adolescents, who are usually late shifted by 2 or 3 hours compared to adults, is going to look barbaric in another 30 years. People think that 9 AM is a "late start" for high school, but it should probably be more like 11 AM. Even the ratios of NREM versus REM sleep change a lot over different age groups.