I see this even with adults. You can certainly toughen up and work long hours and maybe even efficiently. Most people will probably do a better job with less than ~ 6 hours per day at least on intellectual work or learning. If you try to do more you will not be able to sustain it long term with your other obligations in life while staying healthy and happy. As with anything, there are exceptions but they tend to confirm the experience.
I have worked more than 12 hours more days in a row on very hard stuff during e.g. infrastructure migrations that didn't exactly follow a plan for unforeseen reasons and I did an exam the next day after the return from this business trip. I had more similar experiences. I am able to script/ program multiple hours without much in terms of break if I am "in the flow". I also like long walks or just sitting down with people drinking tea and having a conversation even about somewhat deep topics. This is a kind of offset of the peak concentration and performance.
The question about energy and motivation is in my opinion also related to tools and methods and not just long hours and early wake up. At OrgPad.com we learn about new approaches to education in conversations with our users and friends all the time since our 2000+ users are mostly students at elementary schools, high schools and universities. We also have a small but very active community of academics using OrgPad to pursue research and personal development. E.g. a teacher created a large OrgPage with many topics related to chocolate. These are roughly: activities, knowledge gathering tasks or experiments and information. Using this approach you can motivate children and their due to COVID-19 involuntary home schooling parents to discover e.g. whether chocolatey burns: https://www.orgpad.com/s/9l8igw
The teacher who made all that shares her experiences (in Czech) on https://www.youtube.com/watch?v=nyM6l4FHtb0&list=PLs5kSDmhaz...
It seems, the children (and their parents hopefully too) like her approach to digital education a lot. I sincerely think OrgPad.com can help many people with organizing their thoughts and other information and related materials while not sucking their mental energy as other tools and methods do. If you want a short (< 3 minute, in English) taste of what is possible with OrgPad, please have a look here: https://www.youtube.com/watch?v=FtqFWSJT9yw
The question about energy and motivation is in my opinion also related to tools and methods and not just long hours and early wake up. At OrgPad.com we learn about new approaches to education in conversations with our users and friends all the time since our 2000+ users are mostly students at elementary schools, high schools and universities. We also have a small but very active community of academics using OrgPad to pursue research and personal development. E.g. a teacher created a large OrgPage with many topics related to chocolate. These are roughly: activities, knowledge gathering tasks or experiments and information. Using this approach you can motivate children and their due to COVID-19 involuntary home schooling parents to discover e.g. whether chocolatey burns: https://www.orgpad.com/s/9l8igw The teacher who made all that shares her experiences (in Czech) on https://www.youtube.com/watch?v=nyM6l4FHtb0&list=PLs5kSDmhaz... It seems, the children (and their parents hopefully too) like her approach to digital education a lot. I sincerely think OrgPad.com can help many people with organizing their thoughts and other information and related materials while not sucking their mental energy as other tools and methods do. If you want a short (< 3 minute, in English) taste of what is possible with OrgPad, please have a look here: https://www.youtube.com/watch?v=FtqFWSJT9yw