There is no age limit to when you should dock your dogs ears. it
is perfectly fine to crop your dogs ears even when they are fully
grown. some vets may not do it because it will be a longer
procedure but im sure there is a vet that would do it. some people
even get their dogs ears crop when they a few years old. the only
difference from when their older is that the taping would have to
be on longer and the healing may take some time