Imagine a 70-year marriage. The idea may seem ludicrous—after all, most people are familiar with the statistic that 40 to 50 percent of first marriages in the United States end in divorce, and presumably these couples are throwing in the proverbial towel long before they reach their seventh decade of marriage.

Yet, according to Paul Irving, Chairman of the Center for the Future of Aging at the Milken Institute, Millennials are likely to experience longevity far outstripping that of previous generations. At some point, 100-year life spans could become the norm, meaning that even Millennials who get married in their mid- or early-thirties could be staring down around 70 years of shared lifetimes with their significant others.

“Plan for lifelong learning,” advised Irving in a blog post for the Huffington Post. In the article he listed what Millennials should prioritize in order to plan for the (potentially very long) future. “Plan for lifelong work," Irving wrote. "Save and invest for the long term. Take care of personal health. Make our cities age-friendly. Get involved in the longevity economy. Find purpose.”

ATTN: spoke with Irving on the phone about ageism, purposeful living, and 100-year life spans He said that advancements in the fields of medicine, sanitation, and safety contributed to increased longevity for Americans. The longer life spans that these transformations yielded -- and continue to yield -- are often seen as a drain on the economy and the healthcare system. (Yet, Irving reminds us that it’s important to view older Americans as assets to society rather than simply consumers of society’s resources.)

Longer life spans, more reinvention.

"The fact is, however, that by 2030, about one-fifth of the U.S. population will be 65 or older," wrote Jane Wollman Rusoff, a contributing editor for Research Magazine, in the article "How the Age Wave is Remaking Financial Advice."

With longevity in mind, Irving recommends that Millennials not shy away from reinvention. Retirement at the age of 65 has largely gone the way of the wooly mammoth, therefore Millennials and Baby Boomers alike should be thinking creatively about what gives their lives meaning and purpose, and should continue to reevaluate this question as they age.

The 2014 report "Aging and Beneficial Purpose in the 21st Century – The New Longevity Dividend,” produced by the Milken Institute and the Templeton Foundation, points out that “thirty additional years of life expectancy since 1900 means that what was once considered ‘elderly’ is now merely a prelude to decades of potential productivity and contribution." Also, according to the report, living purposefully slows cognitive decline by 30 percent, and people with purposeful lives are more likely to live longer by up to 57 percent.

“Research confirms that beneficial purpose is not only good for the broader society, it's good for personal health,” Irving wrote in the Huffington Post. “Millennials are already involved in charitable and civic life, volunteering, and investing for beneficial impact, and they're beginning to think about the opportunities for later life transition to purposeful encore careers.”

Graduate programs should be taking advantage of largely untapped older demographics, Iriving told me. Today, it might be considered unorthodox to be 40-years-old and start a Ph.D. program, but this doesn’t have to be the case. Adults in their 40s and 50s likely have access to more disposable income than individuals in their 20s and 30s. The idea of getting a Ph.D. and beginning a second (or third) career may not be appealing to a 55-year-old, who plans to retire in a decade. However, if this 55-year-old potentially has another half-century of life in front of him or her, the desire (and the need) to continue working may become inevitable.

Preparing for the future.

Old age may seem too distant for many Millennials to devote much thought to it. However, there are many things to consider from ageism, prepping for a large portion of the population to be of a certain age, to planning for retirement.

The way older adults are treated affects our society, economy and culture in a myriad of ways. Much of the research Irving conducts at the Center for the Future of Aging at the Milken Institute revolves around the fight against ageism.

“In societies dominated by older populations, failure to address systemic age bias and its impacts will not only frustrate the desires of an increasing number of older individuals who wish to remain productive and active, but also will negatively affect economic growth, competitiveness, innovation, and social progress across the broader society,” Irving wrote in the Journal of the American Society on Aging. In another recent piece in the Huffington Post, Irving urged voters not to judge presidential candidate Hillary Clinton on the basis of her age. “It's time we come to terms with growing older in a rapidly aging America," he stated.

The Milken Institute released a report in 2014, “Best Cities for Successful Aging,” that ranks the top 20 large and top 20 small U.S. metros based on eight categories: general, health care, wellness, financial, living arrangements, employment/education, transportation and community engagement. Among U.S. metropolises, Madison, Wisconsin came in first for adults ages 65-79 (and third for adults ages 80 and up).

Millennials working in government and public policy should be cognizant of the challenges and opportunities inherent in making a city age-friendly. Changes to infrastructure and policy that originate now can to make life more manageable for millions of aging Americans: today's elderly population, the upcoming Baby Boomers, and thirty or forty years in the future, Millennials.

When I asked Irving what policies companies need to put into place to make “lifelong work” viable for Millennials, Irving responded that our corporate culture should be devoid of intergenerational warfare. Generations are not in competition, Irving said. This is not a zero-sum game.

To avoid the burn-out all too common culture of “always on” workplaces, which expect employees to be available 24/7, Irving suggested that Millennials cultivate broad world-views (one skill for which liberal arts educations might be particularly valuable), and he again mentioned the potential for reinvention. Resiliency and flexibility are important, Irving said. He also recommended that Millennials learn to integrate, rather than separate, work and family.

As for saving money, that pesky, not-so-optional obligation that debt-strapped Millennials may struggle with, Irving said that Millennials should try to delay spending on houses and cars when possible. Irving acknowledged that our society needs changes to student loan programs and should be rethinking the cost of higher education, but in the meantime, Millennials should try to save what they can.

Savings allow you to take risks, Irving said, to start that business, or go back to school. So bust out that piggy bank (or savings account, if you're really striving for adulthood) and try not to let saving fall by the wayside. After all, you might need these funds for your 70th wedding anniversary.