Skip math classes breh
The car is 6 years old with 56k miles on it. It's an $80,000. I got a steal.
Sorry breh, but buying old luxury cars is a silly endeavor, you're already behind the newest body style which is the entire point of having one. By the time you're done paying it off you'll be 2-3 generations behind and nobody will even think of giving you half of what you paid for it.
I could see if this were a GTR/ZR1 where there's a limited supply so resale stays high, but A8s are dime a dozen. As long as you like it that's cool, but you won't view it as a steal when you have to sell it.