When I thought about turning 40, I imagined myself struggling to keep up with trends, avoiding sugar like it’s poison, and pretending to enjoy kale smoothies. But then, I met Lisa—my colleague who, at 42, looks fitter, happier, and more energetic than half of us in our 30s. One day, as I caught my breath after climbing two flights of stairs (while Lisa was casually walking in heels, unfazed), I had to ask: “Lisa, what’s your secret? How do you stay fit in your 40s?” She smirked, took a sip of her protein smoothie, and said, “I don’t chase fitness. I make it part of my life.” And that was my lightbulb moment. I started observing her habits—how she moved, ate, and lived—and I realized, fitness in your 40s isn’t about running marathons or spending hours in the gym. It’s...