Almost every afternoon last week, I took a very long, very fast walk with intervals of running mixed in; just once, I didn’t bother to stretch when I was done. The next morning, I paid for that. My creaky knees! My knotted calves! There was no forgiveness for my lapse, not the way there had been in years past, when my stretching was reliably unreliable.

Similarly, I get no allowance anymore for evenings of gluttony. Back when I was The Times’s restaurant critic in my early 40s, I could atone for an excessive dinner and erase its effects by just increasing my exercise in its immediate aftermath. Now I need the better part of a week to get back to where I was.

At 58, I reflect often on the differences between youth and age. One of the biggest is the margin for error. You have a big, broad one when you’re young, and that applies not just to muscles and midriffs but also to relationships, jobs and more.

You can be sloppy, and the wages are modest. You can be heedless and recover. You can squander an opportunity and still find another (and maybe even another) and make the most of it, having learned from your mistakes. You have time. You have flexibility. Everything is more elastic — your knees, your calves, your skin, your heart.

Don’t get me wrong: Age has its benefits. I much prefer 58 to 28. As I described in my most recent book, “The Beauty of Dusk,” age can bring a perspective and sense of peace that are so elusive in youth, when many of us are too distracted — by self-doubt, by want, by envy, by vanity — to learn the trick of contentment.

But age also compels us to proceed with caution. To take greater care. The flesh-and-blood vessels that we occupy are more fragile. The promises we mean to keep and the plans we intend to execute can be postponed only so much. Time is of the essence. Which is perhaps why we’re graced with the wisdom to see that.