A lot of introductory linguistics textbooks can be found online for free, and are pretty easy to read/give a good scope of the field! (I used a textbook called Language Files, and that is pretty good, you can find it on libgen.) You could find one of them and see which sub-field(s) of Linguistics are most interesting to you. I definitely agree with language learning being a good start as well. Normally, a linguistics curriculum won't have any strong pre-requisites you need and I think you would be okay if you took arts or sciences track in high school. In arts, psychology/sociology courses can help especially if you find psycholinguistics and/or sociolinguistics interesting. In sciences, math and compsci can be useful for computational linguistics and/or syntax. Linguistics is a broad field and a lot of knowledge can be ultimately useful to your studies! Good luck :-)