Sometime during his mid-60s, my grandfather became one of the all-time great obituary readers. I mean a serious, major obit reader. Each morning, he would fold the page back and work his way down the paid death notices from A to Z.

Everybody in the family assumed that he turned a bit lugubrious in his retirement, in his illness, and was waiting for the cameo appearance of some old friend in the newspaper.

But I always suspected that he was interested in ages not names. I figured that he was tallying up how many of the deceased were his age or older. He was reworking his odds, if you know what I mean.

Frankly I thought it was a little eccentric at the time. But I was about 15 then and hadn't even started reading the engagement notices.

Now I assume that everybody comes upon some time or times in their life when they become aware of their age -- even become age-obsessed. Suddenly, when they read about a person who climbs a mountain, gains a vice presidency, delivers a baby, they are less interested in who the person is than how old he or she is.

Upon discovering that "John Jones, 42," invented the cure for cancer or ring around the collar, they forget the name and remember the number. They start ranking people at the beach, office or cocktail party less by sex, race and national origin and more by peer group.

A single friend of mine fell into a fit of age-obsession when one of her former students got married. My uncle experienced it the first time he voted for a president who was younger than he.

My own moment was less emotional, less political and altogether more physical.

Having spent a good deal of my youth as a minor jock (can a woman be a jock?), I found myself playing prone last fall. I have spent much of the past six months trying to get back, or anyway get my back, into shape. This is a bit like trying to return a pretzel to its original dough position.

During this period I also became obsessed with age, especially my own. Not in a mournful way; in an athletic way.

If my grandfather chose the obit news, I preferred the athletic news. Without the slightest interest in baseball, I became a forties fan: Carl Yastrzemski, 2, Pete Rose and his Grecian Formula, 41, Gaylord Perry and his saliva, 43.

In the world of Movietone and muscle tone I am by now less interested in Arnold Schwarzenegger than Jane Fonda, 44. In ballet I buck the Gudonov tide in favor of the oldie-but-goodie Nureyev, 44.

The culminated in the unseemly glee with which I greeted the Billie Jean King victory over Tracy Austin last week in the Wimbledon quarterfinals.

The 20-time winner played her 103rd singles match in Wimbledon with knees courtesy of surgeons, and a game held together by grit. She beat a kid who called her a childhood idol. Billie Jean won, 38 to 19 (years, not sets).

Maybe people only become obsessed by their age at certain moments when they feel options closing down. They're finally, irrevocably, no longer going to pitch for the Seattle Mariners; no longer going to dance the four cygnets in "Swan Lake." Then we start rooting for the keepers more than the comers, the tenacious more than the precocious. Those our own age.

I think that's what happened to me, anyway. I'll never get back to Wimbledon. I never got to Wimbledon. I'll settle for an hour of decent doubles. But it was great to give Billie Jean, 38, the proxy to keep my end of the court open for the while.

My age-obsession came with a sense of modest physical limits. I suppose my grandfather's came with the fear of death. I wonder if one morning when he was reading the obits, he ever had the same thought that Billie Jean King had at Wimbledon: "Anything now is a bonus."