The notion that a threat to seniors is their peers is somewhat new, and usually played for laughs. It goes against a truism handed down from mothers to daughters for generations: This, too, shall pass. Mean girls are not girls, or mean, forever. High school doesn’t last forever, everyone grows up. But Nanna’s experience suggests otherwise. It says that the cruel, like the poor, are always with us, that mean girls stay mean — they just start wearing support hose and dentures.

A recent Cornell University study by Karl Pillemer proves the point, showing that aggression among residents in nursing homes is widespread and “extremely high rates of conflict and violence” are common. According to the study’s news release, one in five residents was involved in at least one “negative and aggressive encounter” with another resident during a four-week period. Sixteen percent were cursed or yelled at; 6 percent were hit, kicked or bitten; 1 percent were victims of “sexual incidents, such as exposing one’s genitals, touching other residents, or attempting to gain sexual favors;” and 10.5 percent dealt with other residents’ entering their rooms uninvited, or rummaging through their belongings.

Whether you’re brawling on the playground or battling over the best seats in chair-cercize, bad behavior is constant, and the rituals for trying to get in with the in-crowd don’t change much. Nanna’s quest for “the Cadillac of walkers,” a $400 number not covered by Medicare, mirrored my search a decade ago for the nearly thousand-dollar Bugaboo that would signal to my urban-mommy cohort that I belonged.

What transforms with age are the criteria for judgment: not looks, not wealth, not the once-coveted ability to drive at night. When you get to be Nanna’s age, you’re reduced to a number — the younger the better. Even in a residence for the elderly, the 80-somethings will still be cold to the 95-year-olds. Now 99, my Nanna is completely cognizant of what’s going on. Her memory, both short- and long-term, is excellent. But once her new neighbors heard her age, they knew they didn’t want her at their table.

“My question is, are they rude? Are they nasty? Or is it that she’s not hearing, or is interpreting something that’s not really something? I can’t tell,” says Aunt Marlene. “I think there’s definitely cliques. I don’t know if there’s a way to alleviate the feeling of being left out. At 99, do you end up with a group? Does that happen? I don’t know. At first I thought, it just takes time. Now I wonder — maybe this is the way it is. Maybe you can’t expect anything else.”

Bad behavior doesn’t change. Nor does the response from the ones on the sidelines, watching and hoping for the best. Even with lowered expectations, it’s hard. I fret about my first grader getting shut out of the four-square game or my sixth grader sitting alone at lunch. My mom and her sister wonder if their mother is suffering the same kind of isolation, exclusion and loneliness; the pain of having outlived every single one of your contemporaries, of having lots to say and no one to listen.

Nanna tries. Every day, she takes a class: Yiddish, current events, even iPad 101. She gets dressed up for dinner, with a pretty scarf, a new sweater. She’s gotten to know her neighbors, table-mates, even the one who forgets her name between one dinner and the next, and she’s joined a mah-jongg game — “even though I haven’t played in years.” The ledge outside her front door is home to a little stuffed bear, dressed in University of Michigan regalia, a hopeful sentry, and maybe a conversation starter.