Hello Sassy. If you pay off your student loans, that will not affect your AAoA. FICO considers both closed and open accounts in computing one's AAoA, therefore an account going from open to closed has no effect -- whether we are talking about immediate effect, or even an effect 7-8 years down the road. Eventually the closed accounts will fall off your reports in ten years, but that is way way down the road.
That said, paying off all your open installment accounts will indeed harm your FICO 8 score, though by how much we can't guess unless you tell us the original amount of the loan and the current amount owed (for each loan).
As you can see, simulators often given flat out false information that can lead people to attempt expensive strategies that harm their score. Glad you are asking us first.
PS. Mortgage scores are hurt less by installment loan payoffs, but they are certainly not helped.
