I believe the 6 year rule is correct.
I absolutely know that as of mid-year 2003, DC would only allow dealers to write extended warranties on cars THEY sold. The car could have been sold used but the warranty had to be written by the selling dealer, not the servicing dealer. If you bought the car privately, there may or may not be a possibility of having the original dealer sell you an extended warranty.
Soooo, if you bough it from a local dealer, you're in like Flynn.