As Boomers age, they are likely to redefine old age based on their own lives and perceptions. In a recent article for The New York Times, Steven Petrow asks the provocative question, "Am I 'Old'?" and discovers that the answer is entirely different based on who is being asked. Sergei Scherbov, a researcher on aging, answers the question with a broader definition, telling Petrow that "an old age threshold should not be fixed but depend on the characteristics of people.” He sees such factors as life expectancy, disability rates, cognitive function, and personal health as contributing to the definition of old age. Thankfully, says Scherbov, a 65-year old today is generally equivalent to a 55-year old from forty-five years ago.

It turns out that different generations define "old age" differently, too. According to Petrow, we Boomers generally regard 73 as the start of old age, while Gen Xers think it is more like 65 years of age. Meanwhile, Millennials believe 59 is "old."

Sadly, the negative perceptions of elders is a universal phenomenon: Well over half (almost two-thirds) of respondents to an international survey by the World Health Organization "did not respect older people," writes Petrow. In high-income countries such as the U.S., the lack of respect for older people was highest.

Ultimately, we all define old age in personal, subjective terms. Those of us who are spry, active and healthy at 65 or 70 probably perceive old age as far in the future, while Boomers afflicted with health issues or limited mobility may feel differently. Being engaged and vital, having a full and rich life, and feeling useful may all contribute to seeing aging in a positive light.

How do you define "old"? Maybe the best way to look at it is simply, "You're only as old as you think you are."