WHEN David Letterman confessed that he committed matrimony, his studio audience gasped in disbelief. After 23 years of drinking free milk, he decided to marry the 48-year-old cow? (Calm down, feminists, this is a metaphor.)

It would have been less shocking had he become "lactose-intolerant" and sent her out to pasture, as he did with his last live-in.

The 61-year-old gap-toothed goof's marriage to Regina Lasko followed the wedding of late-late-night host Craig Ferguson, 46, to longtime GF Megan Cunningham, 35, and 54-year-old Bruce Willis' surrender to a 32-year-old Victoria's Secret model. (She has a name but the only name that matters is Vickie's.)

Finally, after seven years of cohabitation, 44-year-old Calista Flockhart is now engaged to Harrison Ford, 66, who's pulling in Social Security checks.

For the women, these are default husbands, who have more than maturity in common. They are rich, filthy rich, obscenely rich, Bernie Madoff-rich.

What is it with geezers suddenly sealing the deal when younger men - such as horny singer/songwriter John Mayer and red-necked Levi Johnston - can't be dragged to the altar?

[Editor's note: Probably due to his legendary modesty, Stu neglects to mention that his third wedding anniversary is coming up.]

Are the guys making their long-range, in-home nursing plans? Have the wenches dosed their dudes with a drug that causes them to drop to bended knee? I've heard of Viagra, could this be Maritalipitor?

The second time I married, it was mainly to avoid AIDS. I had had a lot of fun when single-o, but the times they were a-changing. It was no longer a matter of contracting something fun, like genital warts. Getting down with the wrong sexual "partner" in the early '90s was like Russian roulette.

So, I got married to protect my physical health, and sacrificed my mental health. It's easier to live with AIDS than with lunacy.

Because I paid for that mistake for years, when I did find my true (final) love, friends tried to talk me off another marital ledge.

That's what friends are for. Most of them became my ushers.

So, I have insight into why an old dog wants to come in and lie down in front of the fireplace.

So does "celebrity psychiatrist" Carole Lieberman, author of "Bad Boys: Why We Love Them, How to Live with Them." She sees each celeb I mentioned as a unique case.

For Bruce Willis, it was payback. "After years of being jealous of Demi having a hot young spouse, he finally found a hot young clone of Demi," she says.

Letterman "was a commitment-phobe, but finally gave in because he had a son - and heart problems."

Not in that order, but will marriage repair his heart?

Harrison Ford "finally felt secure in Calista's love," says Lieberman. "And they have been dating for seven years, so he got the seven-year itch in reverse."

OK, but is there a trend here (that I can make fun of)?

"The trend is that each of these 'geezers' is getting married a little reluctantly, for more practical reasons, rather than with wild passionate abandon," she says.

OMG! She nailed me!

"Their innocence is gone, but so is their need to sow more wild oats," she says.

Do I have a twin?

For a second opinion, I turned to "Dr. Beyonce," for her "prescription" in "Single Ladies":

"If you like it, then you shoulda put a ring on it."

The old dudes got the message. Or maybe they got a dose of Maritalipitor. *

E-mail stubyko@phillynews.com or call 215-854-5977. For recent columns: