Stuff like that can't really be answered... There will always be possible illnesses and diseases and accidents that we can't avoid. The best thing we can do is take precautions and make sure our dog has the best odds of getting through life.
Things you can do that can help a dog get through to old age:
- Get a puppy from a reputable breeder. This enables you to have the best chance at avoiding hereditary diseases that can lead to a premature end for your pup.
- Make sure your puppy gets all of it's shots and that it remains up to date on them throughout its life. Opinions on this vary but this is mine.
- Don't take you puppy to places with heavy dog traffic until it has at least it's second round of shots. I'm personally paranoid about this because I lost a puppy to parvo, though it was likely contracted from the shelter which is not uncommon for pups that are there for a long time.
- Keep your dog under control at all times. This means leashed in public until you have a solid recall and even then if you're around roads and stuff I would keep the dog on leash. Usually there are leash laws in place anyways.
- Feed your pup good food, but not too much! Lean and mean is best for German shepherds as it helps reduce strain on their joints.
- Exercise! Exercise your dog so that to keep it physically and mentally healthy.
- Proper fencing. Make sure if you let your dog loose in the backyard that you have at least a six foot high fence. Otherwise you should not leave them alone in the backyard in case she jumps the fence.
- If you have a pool that isn't fenced in you need to supervise your puppy at all times when it is out, until you know the puppy can swim. It would also help to show your puppy where the steps to get out of the pool are and then work on guiding your puppy to them so that it knows how to get out if it even slips and falls in by accident.
Hmmmm... I think that's all I can think of. XD Premature deaths, while not perhaps uncommon, aren't common either. So long as a dog is in a healthy environment for the length of it's life odds are it will live to a ripe old age. Don't over think things and get paranoid though, just use common sense and be a responsible dog owner. This'll give your pup the best chance at living a long, healthy life. :3