This advice makes sense... only if you are already fortunate enough that choosing to take unpaid work, buying all your meals out, etc. is a reasonable choice that doesn't impact your personal finances.
For the rest of us, though, we need to get there first. The best advice I have for younger people to help them get there is not to optimize your earnings, but instead to minimize your personal burn rate. It is nice to have enough money for nice homes and other things. It is even nicer to know that if your income went away, you can still live on a low-paying job is you absolutely had to. And it is wonderful to be able to take any job you want, with a high salary being a nice-to-have bonus, not a requirement due to choices you made in where and how to live.
For the rest of us, though, we need to get there first. The best advice I have for younger people to help them get there is not to optimize your earnings, but instead to minimize your personal burn rate. It is nice to have enough money for nice homes and other things. It is even nicer to know that if your income went away, you can still live on a low-paying job is you absolutely had to. And it is wonderful to be able to take any job you want, with a high salary being a nice-to-have bonus, not a requirement due to choices you made in where and how to live.