Many incarcerated people would be the first to acknowledge the pain and loss their crimes caused. But if prisoners older than 50 have served decades-long sentences and have shown evidence of rehabilitation, the only rationale for holding them appears to be endless punishment and retribution.

The problem is growing as the American prison population gets grayer. By 2012, there were almost 125,000 inmates age 55 and older out of a total population of 2.3 million. Even as the overall prison population continues to decrease, it is estimated that by 2030, there will be more than 400,000 over 55s — a staggering increase from 1981, when there were only 8,853.

The numbers are rising despite recognition that continuing to lock up older prisoners not only does nothing to reduce crime, but is also expensive and inhumane. More and more aging people are becoming seriously ill and dying in prison. Prisons are not equipped to be nursing homes.

And there is mounting evidence that there is little, if any, public safety benefit to keeping people like Ms. Rubero in prison for so long. According to recent studies, a vast majority of people over 50 who are released from prison in the United States, including those with convictions for violent offenses, are much less likely to commit a crime than younger people who have never been incarcerated. Nationally, rearrests occur for only 2 percent of former prisoners over 50, and hardly at all among over-65s. Most people simply age out of crime.

If older people in prison pose so little danger, why not free them? As Ms. Rubero’s experience suggests, a major reason is a resistance to granting parole.

The criteria of parole boards in states like New York include assessments of a prisoner’s possible threat to public safety and her chances of reintegrating into society. Yet boards primarily base their decisions to deny on the seriousness of the crime for which the person was convicted.

Overlooking the fact that elderly people who have served long sentences are not a public safety risk, parole boards focus instead on the past criminal behavior. In effect, they prefer to resentence the prisoner rather than make a judgment about the individual’s growth since entering prison.