20,000 miles isn't really great overall but for a "performance" tire probably not terrible.
My 2010 had Goodyear Eagle Sport all seasons on it when I got it. I put 33,000 miles on them and figured they had at least 10K on them when I got the car.
Rears were not quite to the wear bars - (they were when I got to the tire store
) and the fronts were about half wear or a little more.
The fronts were showing some cracking on the sidewalls so I elected to replace all 4 since I will run at higher speeds sometimes. My car is every day driver/toy so the Eagle All Seasons work well for me.
YRMV