I now understand the term “coltish.”

My running route takes me onto the campus of the local high school, and when I run there, in the evenings, the various fields are full of teenagers practicing sports. They seem to be all arms and gangly legs, and they resemble nothing so much as baby horses, playing in a meadow. Coltish: it describes them perfectly.

I no longer resemble a baby horse, and it’s difficult for me to believe I ever did. The last seven years have not been kind to my body. To whit:

A half-dozen pregnancies, half of which lasted long enough to become physical experiences spat up from the bowels of hell. (Cumulative weight gain: about 120 pounds. Number of days spent thinking I was dying: all of them.) Two deliveries, one torturous. Twenty-eight months total of exclusive breastfeeding. Punishing insomnia. And so on.

All of this at an age, and a stage of marriage, when I should be sending my kids off to college.

Several months ago I finally started running again, after four and a half straight years of pregnancies and nursing. The first time I went out, it was as if I had commandeered a stranger’s body, heavy and stiff and foreign. My arms couldn’t get in sync with my legs. I struggled through a mile, stopped, and thought My God. What was that?

But I went back the next day, and the next – five days in a row, that first week, feeling like a cadet at boot camp. My knees ached and my shins splinted and my sides stitched. Over the months, as I lengthened my mileage, I ended up running through that high school, past all those teenagers. And it dawned on me, as my lungs burned a hole in my chest: That used to be you. And now it isn’t.

Profound? No. But I had never been forced to confront it before.

Sometimes one of those young girls runs across my path, chasing an errant ball, and then waits to one side until I have passed. I always avoid eye contact. Not just because that’s my Standard Operating Procedure, but because I don’t want to see what I imagine to be in her eyes, what was in my eyes at that age.

A vague censure. That, or complete indifference.

Wait, I want to call out. I am old enough to be the mother of your older siblings. I’ve had two babies recently…there’s a good reason for the cellulite, for the plodding motion. I don’t sleep well. I’m doing the best I can.

If I feel churlish enough, I’ll mentally cry out, Let’s see if you look so good after a quarter century and two babies!

(Did I mention that I’m operating on very little sleep?)

It’s not these girls’ fault – they probably barely notice me. No, it’s my own mind that provides the negative commentary, the comparisons. Most of the baby weight is gone by now, but I feel so different – I am different. I am no longer young, not like that, certainly not mentally. (Nothing will make you feel older, faster, than trying to lift a 34-pound toddler from his crib when your back is spasming because you ridiculously injured it yesterday while getting out of the freaking car.)

It is difficult to reconcile the changes that have taken place. First I was one person, then – days and years later – I was another, and there was no line I crossed, no light that changed to signal the passage. It didn’t happen to me – one day it just had happened, and there I was.

(Having babies late in life probably condensed all of this, for me. When they scrawl “Geriatric Pregnancy” across your chart, it’s not exactly subtle.)

I will be forty in a few weeks. I feel about fifty, but I am fighting back. I take vitamins, when I remember. Three times a week I pull on my running shorts and my good shoes and my cheap stopwatch, and I force myself out the door. The first twenty minutes are torture, every time, but I persist. For my boys, for myself. I try not to do useless, disheartening math problems in my head. Like, “When the youngest graduates from high school, I will be…this old.” Or “When the oldest has his third child, I will be…this old.”

Sometimes, ignorance is best.

We have many, many miles to go before our babies are up and out. Many years of sports and trips and sleepovers and high energy and noise. I will patch this body and mind back together as best I can, and I will keep going. I will try not to drag. I will try not to act my age.

I have brought forth two boys who dazzle me in every way, and I want to explore the universe with them, for as long as I can.

Fading is not an option.