INSIDE COLEMAN PRISON, Fla. — Twenty-one years into his nearly 50-year sentence, the graying man steps inside his stark cell in the largest federal prison complex in America. He wears special medical boots because of a foot condition that makes walking feel as if he's ''stepping on a needle.'' He has undergone tests for a suspected heart condition and sometimes experiences vertigo.
''I get dizzy sometimes when I'm walking,'' says the 63-year-old inmate, Bruce Harrison. ''One time, I just couldn't get up.''
In 1994, Harrison and other members of the motorcycle group he belonged to were caught up in a drug sting by undercover federal agents, who asked them to move huge volumes of cocaine and marijuana.
After taking the job, making several runs, and each collecting $1,000, Harrison and the others were arrested and later convicted. When their sentences were handed down, however, jurors objected.
''I am sincerely disheartened by the fact that these defendants, who participated in the staged off-loads and transports . . . are looking at life in prison or decades at best,'' said one of several who wrote letters to the judge and prosecutor.
In recent years, federal sentencing guidelines have been revised, resulting in less severe prison terms for low-level drug offenders. But Harrison, a decorated Vietnam War veteran, remains one of tens of thousands of inmates who were convicted in the ''war on drugs'' of the 1980s and 1990s and who are still behind bars.
Harsh sentencing policies, including mandatory minimums, continue to have lasting consequences for inmates and the nation's prison system. Today, prisoners 50 and older represent the fastest-growing population in crowded federal correctional facilities, their ranks having swelled by 25 percent to nearly 31,000 from 2009 to 2013.
Some prisons have needed to set up geriatric wards, while others have effectively been turned into convalescent homes.
The aging of the prison population is driving health care costs being borne by American taxpayers. The Bureau of Prisons saw health care expenses for inmates increase 55 percent from 2006 to 2013, when it spent more than $1 billion.
That figure is nearly equal to the entire budget of the US Marshals Service or the Bureau of Alcohol, Tobacco, Firearms and Explosives, according to the Justice Department's inspector general, who is conducting a review of the impact of the aging inmate population on prison activities, housing and costs.
''Our federal prisons are starting to resemble nursing homes surrounded with razor wire,'' said Julie Stewart, president and founder of Families Against Mandatory Minimums. ''It makes no sense fiscally, or from the perspective of human compassion, to incarcerate men and women who pose no threat to public safety and have long since paid for their crime. We need to repeal the absurd mandatory minimum sentences that keep them there.''
Edmond Ross, a spokesman for the Bureau of Prisons, said, ''We have to provide a certain level of medical care for whoever comes to us.''
At Federal Medical Center Devens, a prison near Boston, 115 aging inmates with kidney failure receive treatment inside a dialysis unit.
''Renal failure is driving our costs up,'' said Ted Eichel, the health services administrator for Devens. ''It costs $4 million to run this unit, not counting medications, which is half our budget.'' Devens also employs 60 nurses, along with social workers, dietitians, psychologists, dentists, and physical therapists. They look like medical workers, except for the cluster of prison keys they carrying.
Down the hallway, inmates in wheelchairs line up to receive their daily pills and insulin shots.
Although the prison houses about 1,000 low- to high-security inmates, they are not handcuffed or shackled, except when being transferred outside the facility. A golf cart has been redesigned into a mini-ambulance.
At prisons such as Devens, younger inmates are sometimes enlisted as ''companion aides,'' helping older inmates get out of bed, wheeling them down the halls to medical appointments, and helping them take care of themselves.
''The population here is getting older and sicker,'' said Michael Renshaw, a Devens clinical nurse and corrections officer who noted the differences between working as a nurse there and ''on the outside.''
''Inmates get very good care here,'' Renshaw said. ''But on the outside, maybe you would give a patient a hug or he would hug you. Here, you have to be able to maintain your borders. It's a prison.''
The Obama administration is trying to overhaul the criminal justice system by allowing prisoners who meet certain criteria to be released early through clemency and urging prosecutors to reserve the most severe drug charges for serious, high-level offenders.
At the same time, the US Sentencing Commission, an independent agency, has made tens of thousands of incarcerated drug offenders eligible for reduced sentences.
But until more elderly prisoners are discharged — either through compassionate release programs or the clemency initiative started by then-attorney general Eric Holder last year — the government will be forced to spend more to serve the population.
Among other expenditures, that means hiring additional nurses and redesigning prisons — installing showers that can be used by the elderly, for instance, or ensuring that entryways are wheelchair-accessible.