There used to be an old saying, “you're as old as you feel.” It was normally said by old people trying to convince themselves they weren't.

But increasingly science has begun to back that up. Sometimes, you see examples of it in real life – ordinary people active and alert into their 90s. Athletes on the field long after peers from earlier generations would have retired.

In Superbowl 49 last February, New England Patriots quarterback Tom Brady had the game of his career at age 37, and no one is suggesting he is close to hanging up his cleats.

Sergei Scherbov, who led a research team studying how people age, says better health and longer life expectancy has turned ideas about what constitutes “old age” on its head.

Time lived or time left?

"Age can be measured as the time already lived or it can be adjusted taking into account the time left to live,” Scherboy said. “If you don't consider people old just because they reached age 65 but instead take into account how long they have left to live, then the faster the increase in life expectancy, the less aging is actually going on."

Scherboy notes that 200 years ago, a person who reached age 60 was old. Really old. In fact, they had outlived their life expectancy.

"Someone who is 60 years old today, I would argue is middle aged,” he says. "What we think of as old has changed over time, and it will need to continue changing in the future as people live longer, healthier lives."

People in their 60s and beyond may have a few advantages the generations that went before them didn't have. Health care services are better than in the past. There is better knowledge about destructive habits, like smoking and poor diet.

Money helps

Today's older generation is also wealthier. A 2011 British survey found a third of people in their 60s said they were in the best financial shape of their lives, compared to just 23% of their younger peers. They took more vacations and enjoyed life more.

Organizations like AARP have promoted the idea of active, healthy people in their 60s, 70s or older, encouraging “seniors” to stay engaged both physically and mentally. In many cases that means working longer, if desired. But that can sometimes present a whole different set of problems.

Bill Heacock, who runs his own business as a seminar trainer, is 61 and has no intention of quitting. But he tells AARP he's worried that his much younger clients have a hard time seeing past his gray hair. Yet he eats wisely, runs 20 to 25 miles per week and weighs less than he did in college.

What's old?

Stony Brook University researcher Warren Sanderson says someone like that should not be considered old.

"The onset of old age is important because it is often used as an indicator of increased disability and dependence, and decreased labor force participation,” he said.

A 2009 Pew Research Center study asked Americans to define when someone is “old.” As you might expect, the answers were wide ranging. Only 32% said when someone hits 65 years of age. Seventy-nine percent replied when someone celebrates their 85th birthday.

per the Daily Consumer