NEW YORK (CNN/Money) - At the same time financial changes have been altering the face of retirement planning, the way we think about retirement has also undergone a dramatic shift. And to make realistic financial decisions about the future, you've got to take these lifestyle, or demographic, changes into account as well.

Today a 65-year-old man in decent health can expect to live another 20 years or so, or until age 85, and in many cases much longer.

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In fact, a 65-year-old man today has about a 13 percent chance of making it to age 95 and 4 percent chance of living to 100.

And women can expect to live even longer on average than men.

All of which means that unlike even the relatively recent past where retirees might spend 10 or 15 years in retirement before checking out, today it's not uncommon for someone to spend 20, 30 or even 40 years in retirement.

In other words, many people may spend as much time in retirement as they did in their careers.

Far from being a time to disengage from life, today's and future generations of retirees will likely see this as a new stage of life, a time for exploration, an opportunity for continued personal growth, a chance to try new sports, hobbies and activities, to spend time with family, to set and achieve new goals.

In short, today's retirees are not going gently into geezerhood. They may play golf, bingo and shuffleboard, but you're also likely to find them making pottery, teaching reading to disadvantaged kids, running charities, writing books, playing baseball and surfing -- both the Net and the Banzai Pipeline at Ehukai Beach Park in Oahu.

The lines between work and retirement aren't as distinct as they once were.

People no longer see work and retirement as mutually exclusive. Indeed, "rehire" may be a better term than "retire" to describe what many people plan to do after calling it a career.

When the Gallup Organization polled 1,000 nonretired Americans in 2002, more than 80 percent said they planned to work in retirement.