My 6th grader is halfway through pre-algebra. Our plan is to do algebra in 7th, geometry in 8th, algebra II in 9th, trig/pre-calculus in 10th, calculus in 11th, and some advanced math in 12th, if all goes well. We may insert an AoPS class somewhere in between, we'll see.
Like Paula above, my son is an older 6th grader (12), so that helps.
If he struggles along the way, we will definitely slow down. But if he's handling it well, we will just keep moving forward. He is planning on pursuing a STEM career, and many students on the same track follow the same advanced math progression.