I worked harvest and was a janitor in college and still had energy to study. I had no time to do anything else but it was strangely “easy” at the time because I had no distractions.
Youth helped me for sure but I did it later in life than most people.
I was motivated because I believed my effort would pay off. That may be easier without the experience of age but I don’t think anyone is excluded from that possibility.
Sadly, some people make poor decisions when they are young and course correcting gets harder the older one gets.