A good deal of media buzz has been generated in recent years over the fact that Maine has become the oldest state in the nation.

In 2009, the median age of people living in Maine was 42.2 years, ranking us first among the states, ahead of Vermont, West Virginia, New Hampshire and Florida, the next four oldest states.

But what exactly does this mean? Median age is only one way of looking at our demographic character, and not a particularly descriptive one since it says nothing about our distribution around that median.

It is more useful, I think, to look at our population in terms of four groups — those under age 18, those ages 18 to 44, those ages 45 to 64 and those ages 65 and older. From this perspective, more striking — and alarming — differences emerge.

Looking first at the youngest and oldest cohorts, it is clear that Maine is near but not at the extremes.

For the under-18 cohort, Maine ranks third from the bottom. The youngest age group makes up 20.6 percent of our total population. This is well below the national average of 23.3 percent and ranks us 49th among the 51 states plus Washington, D.C. Only Vermont and D.C. have lower shares in the under-18 cohort.

In the over-65 category, Maine ranks third from the top. The “senior” group makes up 15.6 percent of our total population compared to only 12.9 percent for the nation as a whole. Only Florida and West Virginia have larger shares of total population in the 65-plus category.

Combining these measures gives some sense of the demographic imbalance in Maine.

For the U.S. as a whole, there are 53 people age 65 and older for every 100 people under age 18. In Maine, we have 76 people 65 and older for every 100 people under age 18. Only Florida, with 79 “oldsters” for every 100 “youngsters,” outranks us on that measure.

Moving to the middle two cohorts reveals an even more extreme imbalance.

In Maine, 33.4 percent of our population falls into the 19-to- 44 category. This figure is far below the national average of 37.0 percent and ranks us 51st among all the states plus D.C. In the 45-to-64 age group, in contrast, we rank first in the nation, with 30.4 percent of the total population — far above the national average of 25.9 percent.

So, while the buzz is about the combination of our “baby bust” and “graying oldsters,” the more immediate demographic threat lies in our first-in-the-nation imbalance within the middle-aged population.

Maine is like a family business with no succession plan. A disproportionately large share of our population is in the experienced working class. Members of this group hold good jobs, own successful businesses, are raising families and serving as the bedrock of communities.

But who will replace them as they inexorably cross the threshold into the “senior” age category? Putting off retirement will only delay the reckoning. And, to the extent that this group begins to “double dip” — start drawing on state pensions or federal Social Security — they will simply increase the burden on the disproportionately small group that follows.

Nor will “blow up the Kittery bridge” efforts to keep all our young in Maine solve the problem.

However successful we may be in increasing the desire for and access to higher education, however many scholarships and tax credits we may create, we cannot solve our current demographic imbalance by looking to our 18-year-olds. We simply don’t have enough of them, and they won’t acquire the experience and skills soon enough to replace our 45-to-64 year-olds.

The demographic cliff we are in danger of falling over is not marked by a sign that says “65-plus.” It is marked by the empty offices down the hall and the empty spots on the assembly line that our experienced workers used to occupy 10 and 20 years ago.

Charles Lawton is senior economist for Planning Decisions, a public policy research firm. He can be reached at:

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