Starting from early to late 30s, the things that you can do change in scale: You start to become able to manage much bigger contexts, and manage many of them and do it much easier. You start to see patterns much easier. You risk less getting sidetracked by tiny parts in systems, organizations, or dynamics and start being able to see how entire systems work with much less effort. You start to easily spot critical and non-critical parts of any complex context, system, or dynamic. That's what makes a lot of things ranging from being a manager to being an expert or building a business easier starting from that point. Yes, you can do these things in your 20s and early 30s, sure, but the cognitive spend for this kind of big-context management is much more significant in those ages and its more tiring to do it.

4 hours of sleep

There is no age at which anyone should ever need or attempt to function with 4 hours of sleep. Its not the amount of things you do that determines the success of a business or organization: Its their impact. Do a million things in a year with 4 hours of sleep while lacking judgment as a result, you will get nowhere. Do 2-3 impactful, well thought-out and planned things, and you will go places.