When young people ask me how to prepare themselves for a life as an explorer, I usually start with asking them to exercise their Explorers Mindset, ( cuz its a muscle, and benefits from a regular work-out), and then I follow up with these two things: 1, Join a Club. and 2, get a Mentor
By a club, I mean a community of like minded people that might help you focus on your goals and move ahead in little ways that you may not know how to or have the incentive to on your own as a young person. Examples I can think o, off the top of my head that are fairly common, include scuba or mountaineering clubs. Ask if there are any members that are scientists. Hang out with them, read what they read, ask questions and offer to help them out.
For the super ambitious, The Explorers Club offers a Student Membership. They have grants and support for students, and bulletin boards that list expeditions seeking members, The Club is located in NYC, but there are a few local chapters around that might make such a connection worth while. I've been a member for 13 years and its really a lot of fun, and a great way to meet other explorers, and just one place that a young person could look for a potential Mentor.
There are so many people in every field of study that have the capability to change a young persons future just by giving a little advice and making a few introductions for them. But the problem is, that young person doesn't know that potentially influential mentor. Not yet, anyway. But its important to be prepared so that if you get a chance to ask for some mentoring, you don't come off like a goofball.
Its really important to have a clear vision of where you think want to go, to be able to communicate it effectively, and to make sure that the people that you know that are in a position to help you progress know what you are interested in, so they can make a recommendation.
I've seen a few applications for internships on exciting field expeditions that were rejected because the applicant was only thinking about how it helped themselves. What skills or abilities do you have that would make you good to have around? How can you help that person achieve their goals? You might find a way to be invaluable to just the person preparing for the expedition you always dreamed of joining.
All the best,