Please see a vet asap. There are lymph glands in this area and any swollen lymph gland should be investigated. Our dog had mild symptoms of lethargy and a fever. You know just not acting like his usually happy self. We saw 2 different vets. The first one put him on antibiotics due to fever. Followed up with him when he didn't seem to get better.
When we returned home ( we were out of town when it began ) about a week later he was still not better. We noticed a lump under his chin. Went to see our primary vet who diagnosed lymphoma. We tried a variety of therapies and might have prolonged his life for about a month. He died 3 months after diagnosis and we probably waited to euthanize him about a week too late. He was in a lot of pain and to see him suffer that last few days was awful. We had contacted a vet to come to our home but he couldn't come until the next day. We weren't ready to say goodbye but he showed us he was ready by biting me (which is something he would have never done). He felt so bad after he realized what he had done. He kept licking my arm the rest of the night while I sat with him and cried. I think it was his way of telling me that he was ready. We miss him so much!! Love you Patch, you will always be in our hearts!
If you are saying that it is mass like it may be a cyst. You can go to the vet and get a needle biopsy done right there and they can tell you. If it is a large swollen area I would get to the vet as well. Good Luck
German Shepherds are prone also to hip dysplasia which leads to them to experiencing pain in later life. I believe your dog has something related to this or a muscular problem. You said that he is not in any pain, I wonder if it is a cyst...I would suggest a trip to the vet also because your dog is a senior and he could have developed some issues related to the age like I said previously.