Get out your pen and paper. Write down all your interests and everything that you think you might be interested in but have never had a chance to try. Be broad, make it a big list. If astronaut is something you think you might be interested in doing, write it down.
Narrow down the list. Ask yourself what three things on the list you would do if you could only do three of them. Keep crossing out the interests that don't fit that description until you're left with three.
Think about the three interests that you're left with. You don't have to cut any of them if you don't want to, but developing one niche talent will be easier than developing three niche talents. If narrowing it down further is too difficult, consider trying anything on the list you haven't tried before. You might discover you're not so interested in that particular thing after all.
Consider the interests you've decided to pursue. Ask yourself how you will develop them from interest to talent. What actions will you take to practice and develop? What equipment or instruction will you need? Studies have shown that it takes about 10,000 hours to become a true expert at something, so you've got a lot of work in front of you.