You're probably right, Annie, but sometimes there's a big component from the dog's temperament too.
We had two young large dogs, one incredibly agile and flexible, the other seemed to be more stiff and reticent. (Both rescues, both mongrels.) We had the opportunity to get them both x-rayed and assessed, so took it.
The vet called us to come and see the x-rays. He said, "Here are the x-rays. As you can see, one dog has near perfect hips. The other has terrible hips; frankly it's a miracle that dog can walk let alone run and jump. Now... guess which dog is which."
You can probably guess too - the stiffer dog had near perfect hips, the very agile dog shouldn't in fact have been able to walk.

We were glad we'd had the x-rays, as it informed us about a potential problem with the very active dog, so we didn't do agility with him as we'd planned. He did become arthritic when he was older - but I mean
much older, 11 years old. I think with him he was stoic to pain because he was part collie, plus he had a lot of muscle which the vet said must be holding the joints together. Only when he got older and his muscles thinned and weakened did he begin to have problems and feel it.