[wslh]

I think OP wants to start as early as possible and thinking of a PhD now where he/she is in high school is a showstopper.

You can take a look at this kind of high school programs: http://mitadmissions.org/apply/prepare/summer because doing it alone is a bad choice.

[argonaut]

On the contrary, the OP is at the exact right time in life to be thinking about these things. If the OP were 35 with a job, that would be the wrong time to be thinking about a PhD.

The OP is a senior in HS, which means they can 1) tailor their list of colleges to apply to to include colleges that are strong in their research interests and have programs for undergraduate research, 2) After they've decided on a college in the spring, they can decide on relevant classes to take, 3) In college they can reach out to faculty about their projects.