Today's workplaces are home to a growing number of Americans who choose to gild their golden years with a paycheck, raising a delicate but still pointed question: Should careers come with sell-by dates? To be sure, workers are staying on the job longer, and often for reasons that have less to do with money than intangibles: pride, a desire to stay engaged, sheer habit. The number of working adults 65-plus has grown steadily since the mid-1980s, reversing a slide that began in the 1930s when Social Security came along. But in some cases, including a few recent, high-profile ones, they may be staying too long. Veteran reporter Helen Thomas, doyenne of the White House press corps, saw her career and reputation implode in June with an around-the-bend rant on Israel. At 89, she was cashiered. Sens. Robert Byrd and Strom Thurmond prompted colleagues and constituents to remark candidly on their fading skills before they died -- Byrd in office at age 92 and Thurmond just months after retiring at age 100. And Supreme Court Justice John Paul Stevens' orations grew stumbling before his June retirement at 90. Such scenes are now played out daily in the nation's workplaces. One office's paragon of skill, judgment and institutional memory is another's fading old-timer, blocking the promotion of talented younger colleagues. But how long is too long? And how do workers and companies orchestrate graceful goodbyes to the timeclock? The question can bedevil human-resources types, especially those mindful of age discrimination. 'The challenge in dealing with an aging employee whose skills have faded or who has lost interest in many ways is the same as with a younger worker,' said Tammeron Trujillo, director of human-resource services for the Mountain States Employers Council in Denver. 'You have to talk with them. But many supervisors don't know how to have that conversation, and it gets delayed until a pain threshold is crossed for the employer.' Working longer isn't always a choice, especially in an economy that pushed retirement funds off a cliff. Among working adults ages 50-61, 60 percent say they might have to postpone retirement because of the recession, according to a recent poll by the Pew Research Center. And 35 percent of those 62 and older say they have already delayed their retirement. But it's not just the current recession fueling the delayed departures. 'Americans are working longer because they are living longer and need income for those extra years,' said AARP Colorado communications director Angela Cortez. There are reasons people work beyond age 65 that have nothing to do with paying bills and everything to do with staying involved. 'I think the age of 65 is so artificial,' said Betsy Hedberg, owner of Denver Career Counseling. 'Most people don't perceive themselves as being particularly old when they get to that age. They feel unnatural not working. It's not just about money, but knowing they continue to contribute.' For Mary Kreutzer, working at age 73 has brought benefits financial and, by her account, spiritual. She retired from Jefferson County Employment and Training Services at age 65, but found she needed extra income. Three years ago she returned to her roots as an educator, teaching at-risk students at McLain Community High School in the Denver suburb of Lakewood. For her, a long career is hardly too long. 'It's made me feel extremely useful,' Kreutzer said. 'The students don't care how old you are if you have something to offer.' Returning to the classroom also allowed her to update her computer skills. 'I look around and see more people my age doing what I'm doing,' she said. 'I'm not alone in my situation.' In 2008, 6.2 million Americans age 65 and over -- 16.8 percent of them -- were in the labor force, including 3.4 million men and 2.8 million women, according to the Bureau of Labor Statistics. This year, the estimated number has risen to 20 percent. That's up from 15.8 percent in 1985. Frank Day, founder of Rock Bottom Restaurants in Louisville, returned as its CEO two years ago after a hiatus in the Virgin Islands. He turned 78 on Aug. 4. 'I never completely retired,' he said. 'I felt my return was needed. We were having some issues. We were over-leveraged. I feel I righted the ship and put us in a good position again.' While Day says his level of physical energy has waned a bit, he still feels mentally sharp and engaged. 'I don't think I'm doing anything a younger person couldn't do, but the converse of that is that I'm still able to do it,' he said. 'I like the challenge, like the action. 'Some days I say I wish I was someplace else, but I've said that on vacation too.' Career longevity varies with individuals and professions. Artists can last as long as they are still creative. Pablo Picasso and Georgia O'Keeffe turned out vibrant work in their 90s. Actor Paul Newman landed an Oscar nomination at age 77. Pro athletes are special cases, given the limited window that is a playing career. Athletes rarely go out on top. For every Rocky Marciano, who exited as undefeated heavyweight boxing champion, there are dozens who stay too long and tarnish their legacies. Baseball fans still wince at the memory of an aging Willie Mays stumbling in the outfield one season too long. At 70, Garry Horle's skills are only enhanced by age. He is an Episcopal priest, serving as interim rector for congregations awaiting the appointment of a permanent leader. He typically serves 12 to 15 months at a church, then moves on. 'This is my third career,' said Horle, who became a priest 13 years ago after long stints in retailing and for the state of Colorado. 'The priesthood is not just a job, it's a calling. I love the people, love the liturgy, love the people.' But he is paid, and the salary is a boon to him and his wife, who is 65 and also works. 'When I retire -- and there will be a 'when,' not an 'if' -- I'll qualify for a pension, which will help,' Horle said. Knowing when to quit can be hard, and a touchy subject to boot. 'People know when they're bored or unfulfilled, but if it's a matter of fading skill, the person may not recognize it,' said Jane Grogan, owner of Career Match Inc. in Centennial. 'They often don't have that self-awareness.' Carrie Payne, a clinical psychologist in Denver specializing in workplace issues, notes that while expertise and maturity are assets for older workers, stamina is an issue. 'The older we get, the harder it is to sustain a high level of drive, although the expectations for that are kind of unrealistic in our society anyway,' she said. Walt Young, 82, retired in 2009 after a 60-year career as a barber. He maintained his Denver shop for nearly 20 years after many of his peers retired, leaving only after his eyesight deteriorated. 'I can't tell you how much I gained by working those extra years,' Young said. 'That was just two more decades of learning. You wouldn't believe what I absorbed from talking with all those customers.' 