I agree. My guy is 14 weeks, and has only been on a handful of walks. Reason being I have a large fenced yard. First walk was a bomb out. He did what your pup did. Second walk, I had a "Duh" moment, and took our other dogs with us. BINGO!! Walks are FUN! There are things to do and things to see! YAY!!
So next time you want to walk your pup, take your older GSD with you. If they hang out together at all and know they are a 'pack' your pup should want to follow. It's easiest with two people. I had my wife walk the girls, and I followed with Grim. At first, he was whining because he wanted to walk with them, not behind. Then, he decided that there was all this STUFF... everywhere...that he wanted to look at, sniff, explore, etc. and the other dogs weren't as important. It can be a pain, but it's useful because older dogs can teach our puppies things easier. If your older GSD is dog aggressive or people aggressive or reactive in any way that you don't want your pup picking up on, then don't do it. However, if your other dog is good on walks and is stable, this is a great way to get the pup used to a leash and walks. I used to want to get a pup out on walks right away. However, I've been doing things a little different with this guy... and spent the first few weeks only working on house breaking and bonding. The result is a pup that looks to me for direction.
If you try this, please let me know how it goes. It went so well for me.. and I'm curious if this will work for any pup. This is a normal puppy thing, though.