On the last page of "Confessions," Dan Greenburg wonders if his infant son Zack will someday grow up to write a book about his father. Greenburg ought to wonder why he hasn't written the book he should have written about Zack.

Greenburg's account of becoming a first-time dad at the age of 48 is a diary-like journey through pregnancy, birth and infancy, and how they feel to a guy who's old enough to be a grandfather. But Greenburg doesn't do justice to the subject, to the language, to his previous performance or to the exquisite joy of late-in-the-day dadhood. "Confessions" is persuasive proof that dictating a few notes each night does not necessarily produce a worthy book.

Greenburg sets out to prove that fatherhood for older dads is somehow different. He proves exactly the opposite. His misadventures with diapers, pediatricians and Jolly Jumpers could have been experienced and recorded by a man half his age.

The only way in which Greenburg grapples with the book's basic premise is to turn it around. He speculates often and well on how much he would have missed if he had not reproduced. But he doesn't even discuss (much less resolve) a host of obvious questions.

Is it easier to handle a first child financially when you are 48? Do you have the stamina, and the sense of starting a long journey, that you wish you had? Can you stand the thought of attending your son's college graduation when you are 70? But Greenburg would rather discuss the lies his remodeling contractors tell him.

Inadvertently, Greenburg does demonstrate one inescapable aspect of fatherhood-at-48. You get tired. And if you're a writer, your writing gets tired, too.

In his earlier work, Greenburg was consistently fresh and spry. But at one point in "Confessions," he uses the word "energetic" to describe five consecutive people -- thus proving that energetic is exactly what he isn't these days.

At another point, he begins five consecutive sentences with the word "and." He misspells "be'arnaise," and consistently fumbles the difference between "that" and "which." When it's time to describe his wife's difficult and scary delivery, Greenburg can do no better than to compare it to a TV doc show.

As for banalities, this book is dripping with them.

"When my little son looks up at me . . . I know that having him is the best thing I will ever do." Dangerously close to Hallmarkish.

"Gaining a pound when you weigh seven pounds is like gaining twenty pounds when you weigh 140." No kidding.

"His smile melts the paper it is printed on." Even allowing for paternal pride, this crosses the line into goo.

But the most irritating aspect of "Confessions" is Greenburg's incessant name-dropping.

Two friends lend the Greenburg family some baby equipment. Who they are is not important to the story line in the slightest. But Greenburg can't resist telling us that they are his "dear friends" Jill Krementz and Kurt Vonnegut. It's cocktail party-ese, not insight.

In the same way, we are battered and pounded with Bruce Jay Friedman swapping dad tales with the author, Avery Corman declaring Zack handsome, Linda Lavin sending congrats after the birth. Is the point of "Confessions" to show us how well Greenburg is plugged into bicoastal chic? It sure seems so.

Nor does Greenburg exhibit the slightest understanding of how his privileged New York life style colors his life as a father.

Zack has been born into a New Yorker cartoon. His dad has a therapy group. His mom has a therapy group. The family has an apartment in Manhattan and a house in the Hamptons, not just a Jeep but a Porsche, too. The parents take Jacuzzis and go rafting in Arizona at the drop of the hat.

Yet Greenburg has the nerve to refer to himself as "middle-class," and to beef about his nanny's moods when most dads would kill to be able to afford a nanny, moody or not. The author actually tries to pass himself off as Everyfather. To put it gently, that's an extreme distortion. Greenburg has had a fatherhood experience more like that of a Hollywood star than that of a Joe Sixpack.

"Confessions" certainly has its compelling moments. A 49th birthday card from Greenburg's mother is a nice across-the-generations touch. For comedy, it would be hard to beat Greenburg's attempt to buy carryout food from a Manhattan singles bar just after his wife gives birth. And it is inspiring to read how lovingly Greenburg and his wife, Suzanne O'Malley, cooperate during the pregnancy and the early weeks of Zack's life.

But this book's reach far exceeds the author's grasp. Maybe Zack Greenburg will someday do literary justice to the family, and to the older-dad phenomenon. His father hasn't.