Even as a youngster, Rollie looked older and wiser than his years. His white mustache sprouted longer by the month, until it flamed from his cheeks like a German kaiser's.
In the last few years, though, the tribulations of age - not just the appearance of it - have begun catching up with Rollie. His keepers are reminded each time they get a look past the Emperor Tamarin's flowing whiskers and into his jaws.
The tiny monkey, used to crunching away on raw sweet potato, has surrendered all but six of his 32 teeth to the toll of time.
At 17, Rollie - a resident of Chicago's Lincoln Park Zoo - is a senior citizen of his species. In the Amazon he almost certainly would never have made it this long.
In captivity, he's got plenty of company.
The Golden Years have arrived at the nation's zoos and aquariums, taking veterinarians and keepers, along with their animals, into a zone of unknowns.
Do female gorillas, living in to their 40s and 50s, experience menopause?
Can an aging lemur suffer from dementia?
How do you weigh the most difficult choice - between prolonging pain and ending life - when the patient is a venerable jaguar who feels like a member of the family?
All those questions hang on a larger one that, until recent years, has been left to educated guesswork.
"How old do animals really live?" says Sharon Dewar, a spokeswoman for the Lincoln Park Zoo, whose keepers adjusted to Rollie's toothlessness by serving him soft-cooked veggies. "That's the million-dollar question."
Zeroing in on the answer takes years of tracking births, deaths and the age of animal populations. But zoos, which have pooled information since the 1970s, are drawing conclusions. For example, records show that the median age of Siberian tigers in zoos has reached 15 years old, up from just over 11 in the two decades ending in 1990.
The increase in animal longevity is no mystery. Just as with people, health care for animals has become much more sophisticated.
At the San Antonio Zoo, keepers noticed that George, a 37-year-old tapir, was slowing down. His legs seemed stiffer and he had trouble getting up. The diagnosis was clear: arthritis.
First they put him on dietary supplements, then a prescription. Finally the zoo called in a specialist who performed acupuncture on George, inserting tiny needles at various medians in an effort to ease the pain.
Since then, George "acts like he's five years younger," says Rob Coke, the zoo's senior staff veterinarian.
Even as zoos improved care, they've also become much more careful and cooperative in managing animal populations, to make decisions about breeding. Keepers focus on more than just keeping animals healthy, creating habitats and social environments that will make them happy and less-stressed.
The result is more robust animals who live longer because life in a zoo or aquarium grants animals an exception to nature's laws of survival.
Fonzie the sea lion
But aging comes with uncertainties, evident in the case of Fonzie, a California sea lion at the New York Aquarium.
For years, he was one of the top performers at the aquarium's amphitheater. But at 21, he's slowing down. He started hobbling. The corneas on his eyes turned cloudy. In X-rays, veterinarians noticed subtle changes in his bone structure.
"You know how it is when you have arthritis and in the winter time your bones creek because it's so damp and cold?" says Kate McClave, who runs the aquarium's onsite hospital. "Well, it's a similar thing for a marine mammal."
Vets moved Fonzie to an indoor pool where the water temperature is closely controlled and put him on anti-inflammatories. Nearly three months later, the eggplant-shaped mammal lumbers in to the checkup room with all the grace of a sandbag. In exchange for a finned snack, he submits to a stethoscope, a few eye drops, an ultrasound and a look inside his mouth.
"This is one of our few patients that will actually say 'ahhhh,"' says Paul Calle, senior veterinarian for the Wildlife Conversation Society, which runs the aquarium.
Careful treatment appears to have eased Fonzie's discomfort. But his days as a performer are probably over. At the aquarium, his seniority is far from unusual. Immediately after his exam, keepers moved on to take a blood sample from Spook, a 43-year-old gray seal believed to be the oldest on record.
Mysteries and doubts
That longevity confronts zoo managers with mysteries and doubts they've never really had to deal with before.
"The simple question was: 'Does a 41-year-old gorilla need to be on birth control?' And nobody really knew," says Sue Margulis, curator of primates at Lincoln Park.
At the St. Louis Zoo, the uncertainties of aging have keepers wondering about Ruffles, a black-and-white ruffed lemur. At 31, he's a sage.
Some of Ruffles' problems are easily identifiable. He gets an anti-inflammatory pill twice a day - he likes it tucked inside a grape - to combat the pain of spinal arthritis.
But there's no easy diagnosis for another symptom. At times, Ruffles seems to be staring off into nowhere.
"Dementia is one of those things that's very difficult to pin down just because we can't use the same sort of testing as we do with humans," says Joe Knobbe, St. Louis' zoological manager of primates.
The best keepers can do is make Ruffles comfortable, including installing a tiny hanging platform where the lemur, who no longer climbs like a young primate, enjoys resting with a blanket.
Many zoos have modified animal habitats to ease geriatric residents into retirement. At the Arizona-Sonora Desert Museum, a black bear named Spike and his sister Missoula are no longer youngsters. The 22-year-old siblings both have arthritis and Missoula gets inner ear infections that affect her balance. They struggled to reach their den on the third tier of an exhibit featuring steep artificial cliffs.
So in December, the pair moved to a new enclosure, with gently graded ramps and a sloping pool. They'll spend their lives there, off-exhibit, while the zoo renovates the old enclosure so that new bears will be able to age in place.