There have been a fair number of young dogs on here who have had arthroscopic surgery for elbow dysplasia and it's usually first seen in pups under the age of one. Even pups whose parents and grandparents have had elbows xrayed and were clear of ED I think have as much as a 12% chance of developing ED. General vets may not be as skilled at reading the xrays for subtle changes as a veterinary radiologist or orthopedic vet. Get second opinions, and have him examined by an ortho vet who can assess him for pain and assess his gait but it's certainly a possibility in an 11 month old.
https://www.vetsportsmedicine.com/upl...-Dysplasia.pdf