We’ve had several discussions that touched on wild vs captive animals, e.g. https://forum.inaturalist.org/t/are-reintroduced-animals-wild/6334
I think there was general agreement that wild animals taken into captivity temporarily and then released would be considered wild again after release. However, I don’t remember us discussing the situation you describe, where there is no prospect of release. My instinct says that an animal that has been captive for 17 years, reliant on humans all that time, and with no prospect of release, is effectively captive permanently now, even though wild originally.
I don’t think setting a fixed time in captivity before an animal’s status changes would be easy or even useful. Perhaps ‘no prospect of release’ could be the trigger for captive status in these cases. Interested to hear what others think.