What advice or guidance would you give to young people today wishing to become astronauts?

I think there is one very simple answer; follow the passion of your heart. What do you have fun doing? What are you interested in? If you learn or do things for some other reason, some secondary reason, for other people, for the sake of something else, without passion, then you are not going to be your best. If you have an interest, if you have a passion, in whatever it is, you are going to put energy into it and do it well.

To become an astronaut, then, I think almost anything you do will lead to that goal. As long as you are good at it and you have a passion for it.