Administering and scoring the tests will also be expensive, especially if you include a writing sample (which you should). You’d also have to conduct it under very strict guidelines to avoid cheating, and change it up regularly. Therefore, to keep expenses under control, I’d recommend a minimum age of 15, and a certain GPA from the two years previous. It would ensure that kids don’t just take it over and over until they pass (this would be expensive) and those who really want out will do well in the years leading up to it.
Why Age 15?
My homeschoolers ( who are NOT unusual homeschoolers) started college at the age of 13, 12, and 13. Two finished B.S. degrees in mathematics at the age of 18.
And...My kids are NORMALLY bright kids who aren't any smarter than any of the kids of any other Freeper.
So you would omit homeschooled kids under your plan?