Also, maybe Steve wanted a lower energy pup and this guy ended up a little bit of the opposite and now Steve's caught off guard! Some people can be well prepared for an average puppy but some puppies are a little more fun than average.
Steve, how about teaching him some really fun things to do besides the usual "sit, down play fetch?" You can teach your puppy basic agility moves which is a GREAT way to take down energy! Of course you CANNOT practice jumps at this age but you CAN teach him to hop over a broomstick laying on the floor. You can have him go through tunnels (I've seen children's crawl-through tunnels for sale), hop broomsticks, get a long, flat piece of wood, lay it on the floor and have him walk over that, eventually you can lay it up on bricks and have him walk over it elevated, just keep in mind that he cannot do any serious jumping and you'll be fine! You can even teach him the basics of jumping through a hoop, except the hoop must be against the ground so your pup basically walks through it. Around 12-18 months of age is when real jumping, jogging, and biking can come into play. But you can teach foundations NOW!
If you want to teach him to pull a cart at one point, put a harness on him and a length of rope on the harness, then tie an empty can (like a soda can) to the end of it so your pup gets used to A) Pulling something B) Having resistance from behind and C) Pulling something NOISY! The weight of a soda can shouldn't have any effect on your growing pup. If your puppy gets used to pulling something so loud an annoying as an aluminum can now, you'll be worlds ahead when it comes time to really training your dog for pulling a cart! Or maybe you just want a really good way to teach things? Start clicker training! Teach your pup that the sound of the clicker = a fantastic treat like hot dogs, then you can teach him just about anything! Work on the usual sit, down, come, then add things like roll over, fetch my keys, go to your place, get me your bone/kong/ball, the possibilities are endless! Your pup already likes picking up a shirt and a sock. Think how useful that will be come laundry time! Did you drop a sock on the way to the laundry? Be thankful you've worked on it with clicker training when you can tell your puppy to go fetch that errant sock!
You have an energetic puppy that wants to do things constantly and also loves to go get things. You have a DREAM puppy, one that seems very easy to train and very motivated to learn. Use this to your advantage! If your pup is bitey, get a tug toy or bite pillow so he can bite something as a training reward! Lots of GSDs LOVE this- in fact, many prefer playing tug, attacking a bite toy, or going after a ball way more than silly treats! You have a star puppy there just itching to be used to his potential.
I wish my dog would pick up random objects and parade them around! That would mean it'd be easier to teach him to pick up random objects on command and hold them!