Shortly before my 37th birthday, my husband, Garrett, and I decided to go to Nicaragua, also known as the land of volcanoes and lakes. We built our trip around a two-day, 20-mile hike up a volcano called El Hoyo in order to see as much of the former as possible. To prepare, we wiped cobwebs off our hiking boots and tried to take the stairs more often.

Arriving in León, Nicaragua’s second largest city, we met our fellow hikers, including Brita and Shelby, who was named for a movie starring Julia Roberts that her parents liked. “I can’t remember the title,” she told us. “The character Julia played was sick, though, maybe with cancer?”

I realized that not only did I know the disease (diabetes) and the title of the movie (Steel Magnolias), I’d seen it in the movie theater. In fact, I may have even driven myself there, which made me roughly twice as old as these girls. Looking around, I started to understand that I was the oldest person on this hike, older than Brita and Shelby’s other friend, older than the woman traveling alone from Denmark, older than the two guides. My pack, already loaded with water, sunscreen, granola bars, pans, uncooked pasta, and a sleeping pad, got heavier.

Our guides were Andrew, about to return to the United States for business school, and Kristi, taking a break from trying to be a model in Canada. They warned that the first part was the hardest. Yet the hike began gradually, through shady pastures. “Why did the cow cross the road?” someone shouted down the single-file line. “‘Cuz it was the chicken’s day off.”

I recognized that the idyll had ended when the jokes stopped. Suddenly we were on a steep dirt incline in the jungle. The heat held us in tenacious, form-fitting bear hugs. The path was wide but rocky, almost a dry stream bed, then it narrowed and narrowed again. I’d been slightly hunched before, due to the aforementioned pack and meandering thoughts about the significance of movies I once saw. Now I was practically nose to nature, so steep was the trail. I was clawing my way up.

As I did, I thought about the Trail of Tears, the Holocaust, death marches under the Khmer Rouge. The inappropriateness of those comparisons. How the money we paid to go on this hike could have purchased 200 ice cream cones or 100 Fantas back in civilization. Icy showers, soft beds, deep-tissue massages.

I spent a while considering the fact that if I’d had a kid at the age at which I could have first gotten pregnant, he would be Andrew’s age. If I’d had a kid at the age at which I became sexually active, the kid would be in college. She’d be a little older than Brita, who had seen the ocean for the first time the day before. How I hoped any child of mine would be as enthusiastic and adventurous as she.

Nearby, howler monkeys howled. Spoonbills and orioles traded barbs. If I could have seen through the vine-wrapped trees, I would have seen more trees. Raising my head required energy I couldn’t spare, so I watched the ground. Dirt, rocks, roots, my hiking boots. Dirt, rocks, roots, my hiking boots. Dirt, rocks, roots, my hiking boots. Dark blue socks that weren’t mine.

Andrew had come to check on me, wearing the rattiest sneakers I’d ever seen. No laces, more holes than fabric, held together by habit as much as anything else. “How you doin’, dude?” he asked. His pat on my shoulder almost knocked me over.

At another point I stopped, wholly unaware that I’d done so. My legs just quit listening to my head. I’d never felt such dislocation. My body had always done what I’d asked it to, probably because I didn’t generally ask it to perspire this much. The van had long since left the drop-off point; there was nowhere to go but onward.

During each and every break, Shelby and Brita twisted leaves into bracelets and looked away. Kristi bounded from rock to rock wearing low-cut Keds. I mostly panted.

There’s the age you are and the age you feel, and there’s nothing like a 20-mile hike on a Nicaraguan volcano to remind you of the difference.

I couldn’t look at Garrett, because I didn’t want to see his suffering, or my own reflected back. He would have carried me if he could, I knew. He’s four years younger than I am. Sprier. He’d probably taken the stairs a bunch of times without me.

We reached the top. We reached the top! I threw down my pack, threw myself down. Tomorrow we’d swim in the lake that glistened far below, a crater filled with freshwater that would seem as comforting as cotton. In the distance were other volcanoes, which rose gray-black from verdant bases. Up here, you would be forgiven for believing dinosaurs still walked the earth.

The inside of our tent smelled like a third person. Its unstated but persistent threat—to suffocate us—propelled me on the day’s final walk, an easy stroll to check out the hole that gave El Hoyo its name. I motivated myself with the knowledge that dinner would be ready when we got back to camp.

Gripping my glasses, I lay on my stomach to peer into a deep seam in the earth’s crust. It stank, more sulfur-y than the tent stench but equally gross. Kristi chucked rocks into the hole, hoping to hear them hit the bottom. Instead, they smashed against the sides. People have died in stupider ways than getting hit in the head while staring into farty fumaroles. So I rolled over and scooted down.

When we returned from this trip, Garrett and I would stop using birth control.
As the sun sent its last rays toward the massive volcano known as Momotombo, we couldn’t imagine the sense of hopelessness that would arrive like a swarm, or the dams we’d need to concoct against frustration and resentment—when month after month, nothing.

All these years I’d assumed that sheer effort trumped everything else. I could shoulder a pack and set off, study or work hard and succeed, decide to have a baby and get pregnant immediately. Before trying to conceive, this hike had been the most challenging physical experience of my life. Before this hike, physical challenges never seemed all that challenging.

There’s the age you are, and the age you feel, and there’s nothing like trying to get pregnant to remind you of the difference.

When I was Brita’s age, I had seen the ocean but not much else. I never would have had the guts to go off to Central America. The most adventurous thing I’d ever done was spending a week hiking around Utah, wearing jeans and smoking cigarettes. In July. Had you asked me then, I would have told you I didn’t want kids, the same answer I would have given you until the day my answer changed.

That night in Nicaragua, Garrett and I would watch a lightning storm from our tent, the front flap flapping in the breeze, neon zig-zags cracking the black sky. We’d toss and turn not from stony choices but from actual stones, not from squishy regrets but from using our rain jackets as pillows.

Ahead of us would be other sleepless nights. And, one night, even further in the future, our son would wake us.

In the morning, Andrew bounded over, barefoot, bare-chested, clamoring something about the sunrise. Grudgingly, our limbs stiff, our heads hazy, we emerged. Later that day two of my toenails turned black and fell off, and someone’s pet coati tried to take a chunk out of my arm. I smile-cried when I got into the hostel’s tepid shower.

There’s the age you are, and that’s the age you are, and there’s nothing like watching the sun come up, with so many promises, to remind you that it’s just a number. Only you, who’ve lived every one of those days, give it meaning.Jessica Allen has written for The Boston Globe, CNN, Mental Floss, The Onion A.V. Club, and The Washington Post (read more at www.jessallenica.com). She lives in New York.