Hi Elizabeth.
You can start thinking like a scientist at any age - you have to watch
what is going on around you, wonder why things are like they are, think
up explanations, and then test your explanations using predictions and
experiments.
To be a professional scientist you have to have at least a college
degree and generally more school after that, so you don't usually get
your final degree until your mid to late 20's. However, students
can get jobs helping with scientific research while they are still
in college and even some times in high school, and science
graduate students always do research as part of their education.
I have never been in space. Not many people have, but maybe you can if you really work at it.
Cheers,
Terry