There is something called The Ortolani test that is fairly accurate in diagnosing dogs with serious hip problems.
I think the test is best performed in dogs while they are sedated, but I know the veterinarians I work for will do it on puppies to just get an idea of whether or not the hips are really bad.
My dog was walking funny at 16 weeks. We did Penn Hip rads but did not send them in, my veterinarian felt they were good enough. I took the rads to see if JPS was needed. Her gait continued to be "weird" and when she was maybe 3-4yrs of age after a horseback riding trip where we were riding everyday I took hips rads and her hips are crappy. She has almost no neck and the femoral heads are rough. She's going to be 7yrs this year and has no muscle mass over her hips and part of her spine. I've always thought it would be interesting to send the Penn Hip rads in to see how she scored, to the average veterinarian they looked fine but it would be interesting to see what a specialist would have had to say. Although I think it also shows that as puppies their hips can be fine, but as they mature the hips can change.
I don't think it would be surprising to see a pug with bad hips at a young age... the breed has a lot of problems.