Many people marry in their 40s—but not many for the first time. I did. Of course being married at the tender age of 44 (and only two months shy of 45) was not earth shattering. Natalie and I had been living together for over a year. She had a son from a previous marriage, and fatherhood seemed to suit me quite well. So I was marrying into a pre-made family—which meant I’d be a stepdad before I was a dad. Artem was best man at our wedding, and he and I share a very close bond. Natalie and I discussed children, and we were in agreement that we would like to solidify our marriage with a child born of the two of us.

We were married on a rainy afternoon in June. Actually, it was more like a monsoon. By the end of July, Natalie announced she was pregnant. Okay, I thought, here we go.

Right away, I began having visions of diapers, poop, vomit, and all the other icky things babies are associated with…by bachelors. Every day, I had to remind myself that I was no longer that guy. I was a husband and father now.

The first challenge didn’t slap me in the face until the eighth month of the pregnancy. That’s when I tried to assemble the crib. Now, I’m a pretty handy guy. My father taught me how to navigate a tool bench. I’ve replaced brakes on my truck and helped a friend finish his basement. But when it came to the crib, I was humiliatingly unprepared. It would have been easier to build the USS Intrepid out of popsicle sticks and 3-inch deck screws. After an hour or so of scraped knuckles and more than a few choice expletives, the crib finally looked like one.

Funny thing: I had no idea that building that crib would one of the easier tasks of daddyhood. All during Natalie’s pregnancy (yes, it was hers, not ours; I contributed in the very beginning, but the pregnancy itself was hers), I would lie awake at night doing the math in my head: At 10, I’ll be 55. At 20, I’ll be 65. And so on. The numbers started to scare me. Would I be active enough when he became a robust pre-teen? (Ultrasound had told us he was a boy.) I knew I had to make peace with this worrisome math and ensure I was capable of the rigors that awaited me before he arrived. Eating right and exercising became a must.

Well, that was more than three years ago. Time has flown. I’m now approaching the last year of my 40s, and Alex is a chatty, energetic fireball. I creak in places I’ve never creaked before. I carry Alex up to bed every night on knees that whinge at every tread. It’s worth it, though, when I get him to his room and he asks to hug a bit longer before I tuck him in.

So am I eating right and exercising? Well, yes. Natalie makes sure we all eat healthy food. As for exercise, I imagine running after a 3-year-old many times a day would equal at least 15 minutes on a treadmill. And picking up several hundred Hot Wheels cars off the floor every night might be the same as a few squats or crunches. Right?

I assumed the physical demands of fatherhood would be the most challenging, but I learned that the biggest challenge has been my ability to adapt. This might be more easily accomplished by a younger man with fewer life experiences and deep-set attitudes toward the world. I mean, daddyhood requires you to be flexible not just physically but psychologically as well. Gone are the days of a Star Wars marathon, a case of beer, and a bag or two of Cheetos. Gone, too, are afternoons of 36 holes at the local course. Pixar and Disney have replaced Lucasfilm and Lionsgate. “Dark Side of the Moon” has been replaced with the “Muffin Man”—and no, I don’t know the guy. And 40-something years later, that poor little spider still hasn’t made it to the top of the waterspout.

Do I miss the rounds of golf and beers with the guys after? Sure. Do I want to go back to that? No way. Lying in bed with my wife on a lazy summer Sunday and having our little guy jump in bed with us is far better. Having my morning coffee while he has his morning milk are moments that I cherish and will always remember. I’m even looking forward to future Sundays when we run out the door at the crack of dawn for soccer practice or Scouts. I hope my Hot Wheels squats and catch-me-if-you-can treadmill runs will keep me fit enough. I’m lucky Alex is a boy. He loves Legos, a perennial favorite of mine. He loves sitting on the couch and watching “Star Trek: The Next Generation” with me even though he has no clue what a static warp bubble is. To be honest, I have no idea what it is either—but we can still share the moment and the multiple times every episode when he points at the screen and says, “OOOH, Daddy, look.”

When you’re in your 20s and 30s and single, you do what you want, eat what you want, drink what you want, and have no concerns about sleep deprivation, body aches, or much of anything else. When you’re in your late 40s and married with a 15-year-old and a 3-year-old, all of that changes. I’ll never look back. My life now is far more fulfilled and fulfilling. Would it be easier on my physical being if my kids were in their late teens or even off to college? Yeah, maybe. But that’s not where I am. I’ll get there soon enough, I know, and then I’ll wish I could go back, maybe, to where I am right now.

In the end, I know I got it right. I was a free-wheeling, fun-loving guy at a time when my friends couldn’t come out to play because they couldn’t get a sitter. Now I’m the one who needs a sitter—but I don’t mind not going out. I’m in bed by 10 every night anyway, and I have a toddler who makes me smile more than any movie ever could and a nightly goodnight hug that’s more satisfying than any pint could ever be.

—Dave was born in England, immigrated with his parents as a boy, and received a BFA from the Maryland Institute. He works in the shipping and shipbuilding industry and is in his last semester at SUNY Maritime College, studying for a master’s in Transportation Management.