Hi there
My sister has just lost her beloved GSD at the ripe old age of 13. Due to complications and an incompetent junior vet she may well have lasted longer but she suffered a gastric tortion which if detected early enough can be treated but will probably raise its ugly head in the future. The age old problem with GSD's are their hips. Puppies are scored when they are around 6 months old and each hip is scored. My sisters dog was exceptional with a 2:1 score but breeders can breed from dogs up to 10:10 which appears quite high.
Good nutrition, lots of excercise and love will help lengthen any dogs life!