If you are interested in becoming a scientist then my best advice would be to go for it! Find a part of science that you enjoy and keep at it. You can specialise in certain parts of science when you sit your exams in high school (e.g. biology , chemistry or physics) and then, if you’d like to go to University, you can choose more things to investigate further. Science is a HUGE topic and you can be ‘a scientist’ is hundreds of different jobs! 😀
Both Jennifer and Martin have covered the main points. I would also say that you do not have to specialise if you don’t want to. I studied a lot of different science subjects at university, looking at how life started on Earth and where it might be in the Universe through to engineering.
But always look for questions that interest you. Why does this work? Why doesn’t that work? How does this work? What can I do to make this better?
Be curious and ask questions. Science always starts with a guess. Do not be afraid to guess, then decide how you could test this guess. Science should fun so find something that you enjoy and just go for it. 🙂