What makes you feel old? Teaching your kid to drive? Rehabbing that new hip replacement? Witnessing Jack retire from tournament golf?

My 40th birthday is looming with all the joy of an unlubricated prostate exam, and it has me in a serious “God-I’m-old” funk, made all the worse by watching The Shark himself, Greg Norman, compete in the Senior British Open last weekend. Norman missed a play-off between Des Smyth and eventual winner Tom Watson by only one stroke, showing he’s still got game.

But man. I remember him winning everything in sight (except the Master’s and a few other majors) in the early 90s. He was a machine. No one had ever hit the ball as far and as straight as he did. Before they were Tiger-proofing courses, they were Shark-proofing them.

Now Norman, who looks little the worse for the years, heads an international business empire that includes wineries, yacht-construction, and of course golf course design. I just returned from Ireland, where I played Doonbeg, a Norman design that has received huge acclaim since opening three years ago.

As old as his appearance in the Senior Open made me feel, Doonbeg made me feel young (younger, at least). You can’t help but feel great standing on the 15th tee of that course, with a 50-yard wide fairway stretched out before you and the Atlantic lapping at the shore just to your right.

So what makes you feel old? For many of you, it will be watching Tiger Woods fade into senior-hood. Or even when Michelle Wie gets married and has kids (if her dad lets her, that is).

Or perhaps it is the realization that you have only one more decade to whittle your 14 handicap down far enough to try to qualify for the Senior Tour, where you can get your butt kicked by a 60-year-old Shark.