I ended up at a 5:30pm spin class the other day. Odd for me because I like to work out in the morning when the world is quiet, and most people are still in bed. Even more strange because 5:30pm is the witching hour, that sensitive and highly unpredictable time of day. Typically, I’m hauling kids between school and practices and tutors. Or I’m at home throwing dinner together, monitoring homework, feeding the dog. I’m spitting out pages for my writing group, trying to ignore the open bottle of wine in the fridge, putting out some sort of fire that’s just flared up. This particular day was rough. My kids, ravenous for summer, were raging about their finals and about the cupboard being bare. Our dog, Diego, had just killed a squirrel in the backyard and its corpse was attracting an obscene number of flies. And then there was my muffin top…overly pronounced in the too-tight pair of jeans I’d chosen to wear that day, bumping up against my arm, again and again, as I aggressively chopped vegetables for a salad. The whole thing caused my mood to spiral, my parenting abilities to vanish. So I did the only thing I could think of. I put down my knife, pulled on some tights, and yelled to my kids, “I’m out of here!” To which I received no response, either because they were ignoring me, or because they had AirPods jammed in their ears. Or, quite possibly, both.

Here’s the thing about a 5:30pm spin class: everyone is under 30. I don’t know where all the 50-year-olds are at this time of day–I can only speak for myself–but it’s not at the spin studio. At the spin studio, at 5:30pm, you’ll find rows of 20-somethings warming up in badass outfits. Collagen goddesses rushing from work to squeeze in a workout before their online date, or their graduate class, or their second job, or some cool event in DTLA. You will not find a stressed out, post-menopausal, garlic-smelling mom, desperate to restore her failing sanity. Seeing all those young women–women with their whole lives spread out before them–I wanted to bail. I wanted to rush home to the bedlam and that bottle of wine in my fridge. But I didn’t, because the bouncy instructor got to me first, shooing me onto a bike as she cranked up the music. Obediently, I started peddling and put in my earplugs. Just don’t have a heart attack, I thought. There’s no way there’s a doctor in this crowd, and I’m pretty sure Brittany won’t know what to do.

It took my body a cranky minute to realize there was no turning back. But soon–thanks to Kendrick Lamar’s “Humble”–my endorphins kicked in, and my stress melted away. In the mirror, I noticed the gal in front of me had fantastic form, and so I followed her lead, pushing myself harder than usual. When Brittany said, crank up the gear, I cranked it up. When she bellowed, stay in third and climb, I climbed. When she commanded us to get into the saddle and sprint at half time, I sprinted at half time. I don’t know what tonic had been slipped into my water bottle, but I was on fire. My legs pumping as hard as they could. My body glowing with sweat. Initially worried about my ability, I was now conquering the class alongside a room full of warrior women half my age. I imagined the selfie I would take afterward, and the pithy caption I would write about rocking it out with the Millennials. I was proud. My heart was full. So much so that as the final song played, I turned to the young woman beside me and smiled. Telling her with my eyes that we were crossing the finish line together, cycling sisters bound by our mutual pursuit of health and wellness.

Stopped at a red light on the way home, still heady from the buzz of accomplishment, the stats for my workout popped up on my phone. Twenty-two out of 24. I did a double take. I knew there were two outliers at the back of the class, a couple of seriously out-of-shape guys taking it slow, just trying to stay upright. They had to be numbers 23 and 24. Which meant that out of the entire group of women, my score was actually the lowest. I was the bottom of the barrel. But how could that be? I’d kept up. Blended in with those under-30 girls. Maybe even rode better than some them. I wasn’t the worst, was I? Instantly, the glow of my triumph faded. My buoyant heart deflated. So that by the time I returned home and parked my car in the driveway, all I could do was brace myself for the dismal mood inside.

I used to believe that claiming your age made you more self-possessed. But I’m no longer convinced. I think numbers confine us. Herd us into convenient categories and impose limits. Tell us when to go to school and when to start a family and when to retire. Numbers try to convince us that we should or shouldn’t do something. That we are capable or not. That our glory days are upon us or that they have sadly come and gone. For forty-five minutes during that workout, I felt ageless. Stoked by the energy of those vibrant women, my brain sent a message of youthfulness and possibility to every cell in my body. Which was then instantly annihilated by the subsequent communication that my effort was middle-aged and subpar. I wonder what would happen if we lived according to our biology and ditched the chronological calendar altogether? Stopped putting candles on our birthday cakes. Threw the generic data out the window. Lead with our hearts and not our heads. Maybe we’d climb more mountains. Take more risks. Reinvent ourselves more often. And, I don’t know, go to more 5:30pm spin classes.