Old people. Can’t live with ’em, but they’ll die soon enough. Right?

As a 40th birthday present for one of my oldest (in length of time I’ve known him and in his age) friends, I edited together a video of four decades of friends giving him props on going “over the hill.” To quote one of his less sentimental friends, who apparently recorded his video after more than a few drinks, “Congratulations, you’ve reached 40, and not many people get there. Now begins your inevitable slide into death.”

His exaggeration aside, the whole thing got me thinking about how different age and aging will be for our youthful generation. Study after study suggests that most of us will live to see years that our parents and grandparents couldn’t even imagine, to the extent that, according to last week’s Washington Post, the average life expectancy for babies born in 2007 is three months longer than even those born in 2006. Try a life-expectancy quiz online, complete with very personal questions to give you a good squirm – I did one through the University of Pennsylvania’s Wharton School – and see your own vitals.

This begs the question. If, hopefully, many of us will be consistently living into our late 80s and 90s, we need to look at the breadth and depth of how those years influence the whole of our lives.

An extra 10, 15 or 20 years could, and should, fundamentally alter the social and personal factors that govern our lives ­– not just when we die or when we retire, but how we live in those younger years. Who among us hasn’t felt the pressure to conform to certain spoken and unspoken requirements of being a certain age? In your 20s, you should be starting a career, dating and looking for a significant other. In your 30s, it’s time to start a family. In your 40s, you need to establish some financial security for yourself. Fifties see the fruit of your labor, and 60s signal a time to retire.

But what if all of those social dictates – dependent, of course, on religion and background and geography and philosophy – are based on a life calendar that is increasingly out-of-date? What if we live healthily to 90? How does that then, in turn, trickle backwards and provide options never available before?

You and I could work through our 60s and into our 70s. We could be spry enough to provide for children at 40 or perhaps even 50.

Then it matters less if you don’t settle on a career or meet someone special in your 20s or 30s. Maybe, then, you decide to do the Peace Corps. Or teach English in Japan or China. Or move to Seattle and paint the seashore. Or go back to school. Or change jobs.

Maybe you’ve been dating someone for years, and your parents are telling you it’s high time to get hitched, but they’re operating from a clock far different from yours. Few if any generations in history have seen such a significant and sudden increase in life expectancy, so it falls to us to ask how living longer alters our path along the way.

And it’s not an easy question. Our society suffers from collective unease when talking about death and dying.

Our vocabulary describes “life expectancy” and buying “life insurance,” but rarely does “death” come into common discussion. When it does, as it has with some of the most vitriolic and wholly untrue rhetoric coming out of the health care reform debate about supposed “death panels,” bureaucracies formed in the new legislation to decide who lives and who dies amongst the elderly, it is meant solely to encourage fear, and it speaks to our country’s consuming inability to live life while considering death.

I’d advocate this: There is no way of knowing when any of us is going to die, and if there was, count me as someone who wouldn’t want to know. But to avoid thinking about death – to hear the statistics and realize that we are, on average, going to significantly outlive previous generations – and to fail to assess our own mortality at a young age is, I think, a serious mistake.

It is time for us to realize that the great sacrifices and advances of the past have offered us uncommonly good health and good fortune, and we must appreciate and take advantage of our new frontier. We must do more with the time we are given.

So to my “old” friend, on his 40th, I say happy birthday. And I wonder how different his four-oh will be from mine.