I have learned, via People magazine, that Mick Jagger has turned 40. This has been as much a shock to my system as learning, after assimilating the fact that he was alive, that Alexander Kerensky was finally dead. I do not liken Jagger to Kerensky, since even rock music pales when compared to the Russian Revolution, but I pass it along as a way of establishing where, as it is said, I am coming from. I am coming from over 40.

I could, of course, pass along a few tips to Jagger about what he can expect. He will get depressed, wonder about what he has accomplished in life and experience the compulsion to run away to the beach with a 17-year-old girl. Since this is what Jagger does anyway, I expect that my advice to him will be worthless and that he might, in fact, get a sudden urge to marry, have children and go into the insurance business. This would be good for him, but bad for People magazine.

Never mind all that, though. What is important is how people like Jagger keep coming along and getting older. They are living milestones in our lives, a way to date our own aging. For me, though, most of these people have not been famous--like the neighborhood cop, for instance. I can still remember the day I approached a cop on the street to ask directions and realized, to my horror, that the policeman was younger than I was.

Now this was a long time ago, so long, in fact, that there were still cops on the street, but I remember the moment well and even--would you believe?--what the cop looked like. He had red hair and faint freckles and all I wanted to do was ask him how come he was dressed as a cop. Cops, I wanted to tell him, were supposed to be old and tall, have an air of authority and be able to give directions without even turning around. They had the whole thing memorized. Wherever they were and wherever you wanted to go, they could direct you there in no more than two turns and two lights. It takes experience to do that.

Milestones follow quickly after that. A day dawns when you realize that you are too old to ever play professional baseball. You look at the statistics and come across some player who was born the year you last painted your house and instead of him being a child, he is a full-grown man with bushy sideburns, a contract with the maker of some athletic shoe and an awesome proficiency with the phrase "y'know."

The same sort of thing happens when you look one day at the personal data of a Playboy centerfold (Favorite Book: "The Prophet") and realize that you have a car that is older than she is. It is a sobering experience, a fantasy-killer that poses the ultimate question: What could you two possibly talk about afterwards?

There is no end to this. I now deal with politicians who are younger than I am and, in truth, younger than anyone ought to be. I recently had breakfast in San Salvador with one of those and feared--which is what people my age do--for the country, suppressing my every desire to call him "son." I get the same feeling when talking to congressional aides, all of whom, by law, have to be under 30 and wear Bass Wejuns.

The list is endless and endlessly depressing. The paper is full of corporate executives who are younger than I am, colonels in what used to be my Army who are my age, television stars who exist only in the pages of People magazine and who are over the hill, thrice divorced and writing books on the meaning of life--at 24 years of age.

It does not help any that my mother subscribes to a service that tells her whenever any of my former classmates reaches a net worth of more than $1 million. ("He's very successful.") And from time to time I come across some quote from some baby mogul about how anyone who does not make a million dollars by the time he is 30 is just not going to make it. I did not make it.

And now Mick Jagger is 40. It is yet another milestone--one for me and one for him. Whatever my problems in coping with his age, it has to be nothing compared to his. It hurts me to know that I am too old to be a Mick Jagger. But it has to hurt him more to know that so is he.