Corrected entry: When Marty goes to see Doc in 1955 we see Einstein as a puppy. This would mean that in 1985 Einstein would be 30 years old. Though not completely impossible (the oldest dog in the world ever was 29) it is highly unlikely.
Craig Bryant
8th Jun 2005
Correction: The dog in 1955 is a different dog. The Doc even calls it by a different name after another famous scientist, Copernicus.
Craig Bryant