I turned 50 this year. It wasn’t nearly as bad as I thought it would be. My body didn’t disintegrate. My mind still makes the roll call. It has been the occasion of some trifling contemplation. At 50, you are at the crest of your life. That means you can, for the first time, see both ways — backward well enough to see your mistakes and forward well enough to know that you’ll make most of them again. At candid moments, you admit to yourself that the end may be sooner than you?d like.

Statistics suggest that you’ve lived more years than you will again. And probability tables aren’t the only things that are against you. So is Mother Nature. Aching joints, weakening eyesight, and the dismal retardation of your fat-burning hormones. —- Dr. Sears (I mentioned his 6-point approach to good health in Message #290) tells me that the degradation that comes with aging is biology’s way of encouraging us to pass on critical information to our offspring.

In other words, there is no biological reason why we have to weaken before we die but there is an evolutionary one: We are made to fall apart so the younger generation can take over. Unless the oldsters get weaker, they won’t allow the youngsters to take over and won’t pass on to them the knowledge that’s needed to do so. Well, I’m all in favor of letting my kids take their rightful places in the world. I just don’t see why I have to do that by becoming enfeebled.

When your knees start aching with every step you take down the stairs, the natural response is to (1) slow down and (2) bitch about it. But when I think of the older people I admire, there is none of that from them. My dad. My grandmother. My former partner. My accountant. As Anna Quindlen asserts in her new minibook, “A Short Guide to a Happy Life,” the recognition of mortality can be “one of the best things that can happen to you.” That’s the way I feel. I’m not going to move into my next 50 years passively. Why should I?

The human body, I am told, is made to last 120 years. I’ll take 85% of that happily. And I’m not talking about merely staying alive. I’m looking for a little more than that: fun and profit. There is historical substance behind my optimism. Consider, for example, Aristotle, who spent most of his youthful years wandering around in the shadow of his mentor, Plato. Contrary to what most believe, he didn’t figure out his own philosophy until he turned 50 — and then became the most influential thinker of all time.

Henry Flagler didn’t start his railroad project until he was 70 and then went on to develop the entire state of Florida almost single-handedly. And John Glenn, who became famous in 1962 when he piloted America’s first manned orbital mission, was elected to the office of senator (from Ohio) at the age of 53. And at the age of 77, 36 years after his first NASA flight, he became the oldest man in space when he flew on Space Shuttle Discovery Flight STS-95.

At one time, a life span of 50 years was considered full. Today, more and more people are living past their 100th birthdays. So why not think of this benchmark, the 50th birthday, as the beginning of a second life? A second chance? At 50, you are starting all over again — but with the advantage of 50 years’ worth of experience. You can do just about everything you ever did, but with more wisdom to guide you and more perspective to enjoy yourself.

If, like me, you’ve hit (or passed) the 50-year mark, celebrate your new life and promise yourself that the next 50 will be better, busier, and happier than ever. Promise yourself that you will be smarter . . . and stronger . . . and looser . . . and quicker . . . and thinner . . . and healthier. Do more and be more. The hell with what the statisticians told us to expect!