Japan's petty thieves aren't all miscreant teens and wayward adolescents. They're grandparents.

The share of crimes committed by the elderly in Japan has risen dramatically in recent years. According to 2015 data from the National Police Agency, 5.8% of arrests in 2005 involved people 65 years or older. Within the decade, that rate had risen to 20%,the AFP reports.

As more of these senior citizens get locked up, experts say, the more Japan's prisons are turning into nursing homes.

With increasing numbers of older citizens getting locked up, their needs are beginning to dominate prison staff members' day-to-day responsibilities. Personnel are required to help senior inmates bathe, get changed, and clean up after themselves.

"It's a problem that the work of prison officers is becoming more like nursing care," Justice Ministry official Shinsuke Nishioka told the AFP.

The spike in petty crime (mostly shoplifting) can be traced to a number of factors, researcher Yuki Shinko recently told NPR. Increasingly, the elderly populations feel lonely, bored, and unafraid of the legal ramifications. Many have even come to see prison as an upgrade from their daily lives.

"If you are arrested, you still get a roof over your head, you're fed three times a day and you get health checkups. So it's sort of a win-win situation either way," Shinko told NPR.

The Japanese government has set aside nearly $500,000 to hire additional nursing staff at half of the country's 70 prisons come later this April, AFP reports.

Seniors in Japan often struggle to find meaningful work. Many of Japan's companies still rely on the structure of lifetime employment — once somebody jumps ship, it can be nearly impossible to reclaim their place in the hierarchy in old age. As a result, many of Japan's seniors perform low-skill, low-wage jobs. Prison offers a respite from that drudgery, replete with healthcare and financial security.

The incentive to shoplift isn't going away any time soon. Nearly 27% of Japan's population is above 65 — a proportion that could rise as high as 33% by 2035 — so there will soon be even more seniors exposed to the same incentives that elderly people face today.

Plus, younger generations are increasingly prioritizing their professional lives over starting families — fertility rates are so low in Japan that the population is actually shrinking. That has created a vicious cycle economists refer to as a "demographic time bomb," in which younger generations' consumption and social security payments aren't enough to support the elderly. The economy begins to shrink, leading to an even greater emphasis of work over family, which creates even fewer consumers, and so on.

Perhaps the most troubling short-term aspect of Japan's geriatric crime wave is that rising arrest rates compel prisons to make facilities more accommodating for the elderly. In turn, that makes them more appealing — obviously the wrong incentive for aging citizens.

The government also faces a unique challenge, since the mission of reforming criminals isn't a viable option when many won't be alive for much longer. In some cases, officials just have to make sure prisoners remain healthy, and hope they don't re-offend once they're out.

So far, that hasn't turned out for the best. Government data show the recidivism rate for 65-plus is about 70% within five years.