There are a lot of pieces to the puzzle missing, but if it is just money sitting in your (student) account on the day you file the FAFSA, yes it would reduce your federal aid (if you qualify). If you won’t be 18 before you file FAFSA the first time, I don’t know how you’d account for it. If you turn 18 before you need to file FAFSA, you could, as someone suggested about, put it into a 529 account and it would be assessed against your EFC at the parent’s rate, 5.6%. You could also spend it before you file by buying a car, computer, or even a house.
But before you do anything, find out if it will even matter. Run a FAFSA without the asset and see if you qualify for any financial aid. Then run it with all $20k in a savings account (as a student owned asset). Then run it as if you put it in a 529 account (so it will count as a parent asset). Any difference in the EFC?