PITTSFIELD -- Christine Faber, 55, works with seniors every week as a yoga instructor, but even as her 60s approach, she doesn't consider herself "old."
Faber said she has no plans to retire and hopes to work into her 90s.
"For me, I am always thinking about the future, and I don't worry about being a senior," said Faber, who added: "I feel healthy, I am eating right, and I don't expect much change."
The transition to the "senior" category can be difficult for many adults in their 50s and 60s when they remain healthy and active, mentally sharp, and are still working -- conditions not always associated with seniors.
But just what is the definition of a "senior citizen" or "old age"?
The Massachusetts Executive Office of Elder Affairs sets 60 as the senior benchmark, but government agencies begin offering benefits to older adults at varying age levels. For example, Medicare, the federally subsidized health-care plan for seniors, is available to individuals 65 and older.
The Pew Research Center found that the definition of "senior" differs depending on whom you ask. According to a 2009 survey titled "Growing Old in America: Expectation vs. Reality," 18- to 29-year-old respondents on average said old age begins at 60. Meanwhile, respondents 50-64 generally said the threshold is closer to 72, while respondents 65 and older said old age doesn't start until 74.
In the survey, which polled 2,969 individuals, respondents in all age groups agreed that signs of old age include failing health, the inability to live independently, no longer being able to drive, and difficulty climbing stairs.
Other potential markers include forgetfulness, retirement, becoming sexually inactive, getting gray hair, and having grandchildren.
In the same survey, nearly half of the respondents age 50 and older said they feel 10 years younger than their chronological age.
The Ralph Froio Senior Center in Pittsfield serves adults 55 and older. Joseph Major, who is 64 and handles outreach and other programs there, said some employees at the center have suggested omitting the word "Senior" from the name because of its perceived stigma.
On his next birthday, Major will be eligible for Medicare, but he shakes his head when asked if he feels old.
"What are the hallmarks of being a senior?" Major asked rhetorically, dismissing age as a factor.
Older adults say chronological age shouldn't be a defining characteristic.
Jennifer Michaels, a psychiatrist at the Brien Center for Mental Health in Pittsfield, said she routinely meets elderly patients who demonstrate "a rejection of the antiquated view of ‘growing old.' "
"Just because there is a number assigned like 90, 80, or 75, it could have so little relevance in the way of lifestyle or self image," said Michaels, who said her patients associated old age with dealing with a medical condition.
Geriatric psychiatrist David Steffens, professor and chair for the department of psychiatry at the University of Connecticut Health Center, said the word "senior" doesn't match the sense of fitness many feel as they enter their 60s.
"[There are] people in their mid-60s that still have their vitality and haven't appreciably changed much over the prior decade and don't consider themselves as old," said Steffens, who also serves as president-elect of the American Association for Geriatric Psychiatry.
Steffens said as people age, their concerns have a common theme: "uncertainty." Entering their 50s, older adults could be assisting aging parents, so they get a glimpse of that uncertainty.
Depending on their health, older adults will become more dependent on others. And end-of-life issues need to be decided. But Steffens simply described the senior years as "the next stage of development."
"They aren't there yet," he said about people in their 50s. "They are starting to think about issues of legacy, but they are still productive and they are still trying to move forward."