When your GSD pup reaches the teenage stage you might find that it turns into a right lunatic! Sadly this is the most likely age that they will be abandoned because their owners do not account for these stages and decide they have had enough of their hyper/destructive ways. Consistent training and neutering will help you get through this time.
Feeding your adolescent GSD
GSDs of up to a year should be weaned off the 3-4 meals a day and down to 2-3 meals a day. The should be on a good quality puppy or junior diet. Once your GSD reaches one year (remember they don't mature until at least 2) you can switch them over to adult food.
Exercising your GSD
Because the GSD is a large dog its bones are still growing. You should still control its exercise regime. Remember this rule: five minutes for every month. Example: An 8 month GSD should be exercised for 40 minutes at least twice a day.
Your adolescent GSD's health
You should have implemented a tooth brushing and grooming regime by now. Keep this up. They might become difficult whilst you are doing this but be persistent!
Training your adolescent GSD and its behaviour
Continue with your training and socialisation with other dogs. If you began training your GSD as soon as you got him/or him you should have the basic commands down. Why not mix things up a bit and begin training with a clicker? This will help you a lot with recall, which GSDs have trouble with as they enter puberty. Why not try training classes too? Or even agility and flyball classes?
Chewing should hopefully subside as your pup will have its adult teeth by around 7 months.
Males in particular will start to cock their legs and scent mark, maybe even around the home. They are likely to become less obedient, easily distracted and interested in other dogs. He will become much more independent and may even be aggressive towards other male dogs. He might even mount other dogs, you or even the family cat. If this gets too much for you, I advise for you to neuter as soon as possible.
You should have little or no trouble with females during this period. However, they will become very disobedient in the weeks leading up to their first season.