Adult hamster can still get wet tail but it is much rarer because of the immune system issues and the movement issues listed above. I read info about it on
Welcome to the British Hamster Association Web Site when a hamster I was caring for had wet tail. Luckily he made it through but only because it was caught very early by a vet.
Edited to add - My sisters hamster was also hamster sat for a day (she came over to look after him check in and feed on a night away) and she spread the disease from her baby hamster to an adult hamster of 3 years old, the only reason I can say by certainty that it was wet tail is because the vet did a test on the bacteria present and it was e-coli we requested the test to be sure and our vet at the time being a small village vet was happy to oblige knowing we took in a lot of rescues etc. (I wish the busy London vets were as helpful!!!)