There’s a colorful old expression favored by cattish biddies. They let it fly when they spy a middle-aged woman sporting the flashy or revealing clothing you’d normally see on a much younger lass.

“Mutton dressed as lamb,” the harpies hiss, straightening the seams of their own sensible vestments and clomping away in their Easy Spirit mid-heel wedges.

I confess the phrase has been flitting, uninvited, through my head lately as I get dressed:

Hmm, the miniskirt today? Maybe, Ms. Mutton. Or the skinny jeans and pirate boots? Sounds great, Mutton Mama.

Mutton, if you didn’t know, is the meat of old sheep — although the sheep prefer to be called “mature.” It’s tougher than lamb. It’s cheaper. And according to one online cooking site, “Many find it distasteful.”

Since tough, cheap, and distasteful describe me and most of my girlfriends — and since, at 42, I just received a heck-yeah birthday gift card to Forever 21 — I have to wonder if I’ve skidded right over that lamb-to-mutton line without knowing it.

Is this the year they’ll drag me from Macy’s juniors department and shove me into the Charter Club section to collect my tailored capris and nautical tees? Dear god.

The Daily Mail — arbiter of nothing significant, ever — once published a survey decreeing that broads should stop wearing tube tops at age 33, leather pants at 34, miniskirts at 35, see-through chiffon blouses at 40, knee-high boots at 47, and the list goes on.

But since that seemed stupid, I asked my girlfriends for insight. Their responses were as varied as their skirt lengths:

… My 21-year-old son said to me recently, “Where are you going dressed like it’s Coachella? Don’t you know you’re halfway to 90?” I didn’t know whether to laugh or flip him off as I headed out the door. …

… A micro-mini and a deep cleavage reveal do not go together after 40 — choose one or the other. …

… Women should wear what makes them feel confident and secure, regardless of some societal stereotype. …

… But there’s a line between feeling confident and looking desperate. …

When one old (er, mature) high school buddy of mine complained that the only fashion choices at our age are “way immature or near retirement,” a mutual friend interjected, “Girlfriend, if I catch your hot body in a Chico’s, I’m staging an intervention.”

Here’s what I think. We lamb-dressers — henceforth, let’s call us frilly mignon — aren’t trying to compete with twentysomethings or to fool anyone into thinking we’re younger. We don girly getups for three reasons:

1. We know better than anyone that we’ll never again look as good as we do right this very minute. Peeking back at old photos, we’ve come to realize that we didn’t appreciate what we had while we had it — and that two years from now, we’ll have even less of it. So we’re gonna show it off a bit longer and maybe even a bit louder, thank you very much.

2. Putting on something you wore when you were young — short shorts, say, or a backless halter—is like listening to a song you loved when you were a girl. It’s a slightly-too-tight time machine that helps you recognize the old “you” within. And she’s kind of a hottie.

3. Frankly, we were too insecure to wear some of this stuff back when we had the bodies to pull it off. Now we’ve got the chutzpah but lack the muscle tone. Go figure.

Or as one of my girlfriends says, “I’m currently vacationing and have loaded my 44-year-old boobs into a tube top, so I should probably stay out of this discussion — except to say that as I get older and less self-conscious, I think it’s good to teach our daughters that not every flaw needs covering. And if I have three folds in my armpit, so be it.”