Age and sleep

When we are very young, we sleep almost all the time. As we age, that sleep-requirement decreases, until we reach our baseline at about 20 years old, often even still decreasing a small amount from there. As such, anyone under the age of 20 has a naturally increased sleep-requirement compared to their "true" baseline. For people without RSR, this means needing to sleep more than 7.5h. This is combined with puberty, where body and brain are developing and any disruption can be permanent.

Because of this, it is absolutely not recommended for people under the age of 19 to reduce to lower than 2h below their monophasic baseline, and not below 6h in general. People under 17 should stay above 7h at all times. Schedules like Biphasic-X are the only ones recommended under 16, unless TST and consistency must be traded off due to environmental factors, in which case sleep times of down to 6h may be better than inconsistently getting more than that.

Age	Minimum sleep
<13	Non-reducing, avoid alarms
<15	8h or alarmless
<17	7h
<19	6h
>19	5h

Old age, Illness

As we age or when we are ill, the body can start to require more sleep. However, after puberty, long-lasting damage is harder to cause and therefore, being careful to look for signs you cant-adapt (as you should always be doing) is usually enough.