For many years, 65 has been referred to as “the standard retirement age” or by similar terms, even though retirement is hardly standard from one person to the next, much less across time.

The reason that age was picked out was that it traditionally was the age at which someone could begin Social Security and get standard benefits—what is called the “full” or “normal” Social Security retirement age.

That same number was adopted when the Medicare program was created in the 1960s—65 is the age at which Medicare eligibility normally begins, the main exception being those who have certain health conditions.

The concept of 65 as the standard age traditionally didn’t apply to federal employees, however, since eligibility to draw benefits depends on a combination of age and years of service. The oldest age among the combinations is 62, and in fact for many years the average age at which federal workers retire is around that number. Actually slightly below, but far above the general perception among the public.

Also traditionally, claiming Social Security was not a big issue in the federal workforce because the CSRS does not include that feature. But nine-tenths of federal employees are now in the FERS system, which does, and that share only will go up as CSRS people retire and are replaced by FERS people. While only a slight majority, about 54 percent, of new retirees are under FERS, that system’s share of new retirements only will continue to rise, too.

The 65 number lost some of its luster in recent years, though, as the “full” Social Security retirement age started creeping up. The increase began in 2003, when it phased up to 66 over six years. Starting in 2021 it will again begin a six-year rise until it hits 67. That’s a result of Social Security reforms of 30 years ago that are the very definition of the term “long-range phase-in.”

As that increase has happened, more attention has turned to a provision of Social Security policy that allows benefits to begin as young as 62, although reduced. The formula is designed to make the total amount come out about even, taking into account the life expectancy at different ages.

One aspect of Social Security not drawing much attention is the flip side: by delaying the start of those benefits, the payment amounts are increased. That happens until age 70, after which there is no further increase and thus no more reason to delay drawing Social Security.

That “delayed retirement credit” provision was first added to the program in 1972, incidentally, and was sweetened afterward. Again, the formula is designed to make total benefits about even over the average lifetime no matter what age benefits begin.

Meanwhile, there has been much consideration given to raising the Social Security full retirement age further—probably phased in, as well—as a means of putting the program on more solid financial footing long-term.

Overlooked in those considerations is a practical consideration, according to the Center for Retirement Research: benefits payable at age 70 are the largest amount a person can receive, meaning the question is whether it makes sense to draw them at any earlier age. The official full retirement age of 66 should not be used as a starting point for the decision, when in fact 70 is the age at which the system “pays a benefit that serves as the base for a secure retirement,” it said.

For every $1,000 in monthly benefits payable to someone beginning at age 70, for example, $818 would be payable to someone beginning at 67, $707 to someone beginning at 65, and $568 to someone beginning at 62.

“Given that Social Security is a particularly valuable type of income – inflation adjusted and lasts for a lifetime – it generally makes sense for workers to postpone claiming as long as possible to get the highest monthly amount, assuming they are in good health for their age,” the study said.

It noted, for example, that life expectancy for a 65-year-old is now about seven years longer than it was in 1940—up to 19.3 years for men and 21.6 years for women. Similarly, a calculation based on maintaining the ratio of working years to retirement years also suggests a target age of around 70.

“The maturation of the delayed retirement credit has created a new Social Security benefit structure,” it concluded. “Work¬ing until 70 is the way for people to have an adequate benefit on which they can build for a secure retire¬ment. The shift to age 70 may be appropriate given the increase in life expectancy, health, and education for the majority of workers, but it will lead to low replacement rates for the many workers who retire early.”