Jesus told a parable in which the workers who came at the last hour of the day received the same pay as those who had worked all day. Those who had spent the whole day working felt that they were being ill treated.
We usually take Our Lord's story to be telling us that people baptized on their death beds will receive the same heavenly reward as those who had been faithful all their lives.
However, those who were slighted after working all their lives could refer to well- trained, and competent workers who are pushed aside by younger people who have only the advantage of having more years of working left in them.
Akin to those disappointed elders would be all older people who are no longer appreciated.