It's no secret that I'm getting older, and so are my pets.

But only one of us is able to retire, and it ain't me.

At my house, it's AARP, or the American Association of Retired Pets.

By way of background, I've always had dogs and cats, as well as the usual menagerie of pets that populated Francesca's childhood, like guinea pigs, gerbils, and even a pygmy bunny named Peewee, who lived to be 12 years old and had one tooth that actually grew outside of his mouth and up his nose.

Yes, that happened.

Luckily, my vet was able to snip the tooth both times, and though it grew back, at least Peewee got some oxygen.

It's tough to breathe with a tooth up your nose.

This background is by way of saying I'm familiar with pets and how wonderful they are, how much they can love you, and how much you can love them in return, as well as the sad fact that they pass away. I have had all of our pets cremated, and their remains are in my office as we speak, stored in little cedar chests with a sympathy card from the vet.

Shout-out to all the vets who do thoughtful things like writing a sympathy card to pet owners when their pets pass away.

I know pets die, but what is coming as a surprise as I've gotten older is that my pets are aging along with me, and in the past, I always felt that my age was a constant, that I was in temporal standstill while my pets got older and passed away.

But that is no longer the case.

This revelation dawned on me only slowly, when I realized that my back was a little achy in the morning. It happened because I'd been on deadline, so I'd been sitting a lot at the computer, and, of course, the first thing that gets jettisoned when there's work to be done is exercise.

In contrast, there's always time for meals.

In any event, I got out of the chair yesterday, feeling sluggish and unsteady, and I stumbled just a little. At the same moment, I just happened to look over at Little Tony, who had gotten out of the chair because I did, and he stumbled a little before he stood up.

The comparison was undeniable, though only one of us has fur.

(Me, on my legs.)

And then I thought about the relative ages of the pets, realizing that Tony, whom I still thought of as a new dog, was about seven years old and that Ruby is even older. I got her when Francesca went to college, as a daughter replacement.

It almost worked.

I realized that Ruby is almost 13 years old, and obviously infirm. As I've written, she has developed degenerative myelopathy, which means that her back legs are paralyzed, and she has to use a wheeled cart to walk.

Still, she gets around better than I do. I had some ramps built at the front and back doors, and she shoots down them like she's at NASCAR. In fact, she speeds everywhere around the house, and she crashes ahead willy-nilly.

Yesterday, she ran over Tony.

Ruby is a bad driver, even for a dog.

But she still needs special care, and I have to take her out of her cart and lift her upstairs, or onto the bed, or outside to go to the bathroom. She weighs 35 pounds, and I confess to you that in the old days, I might've complained about having to lug her everywhere.

But I don't feel that way anymore.

I feel more tender with her than I ever have.

I get her, now.

She's feisty, funny, smart, and accustomed to doing everything for herself, as well as running the house.

Sound familiar?

And she still feels that way inside, but her body is undeniably aging.

Check, check, check.

I feel sorry for her that she's no longer the undisputed queen and is sometimes even ignored.

Every middle-age woman knows what it's like to feel marginalized.

And we don't like it.

The more I perform these tasks for her, hugging her close, the more I have come to feel a tender kinship with her.

She needs me in a way she didn't before.

And I realize how much I need her and value her particular brand of feistiness, which persists despite all common sense.

I know I will cry when Ruby passes.

And I will have her remains cremated and stored in a cedar box behind me, with a sympathy card written by a vet who sees her only twice a year but still understands how I feel to lose her.

Because that loss will come hard.

Maybe even hardest of all.

And now I know why.

Look for Lisa and Francesca's latest humor collection, "Does This Beach Make Me Look Fat?" Also, look for Lisa's new Rosato & DiNunzio novel, "Corrupted," in stores now. lisa@scottoline.com.