Today is my 40th birthday.

It feels strange to write those words—to acknowledge that in the quiet hours between a summer sunset and sunrise, I passed from one decade of life into another. Here I am sitting at the same table on the same patio as yesterday, with the same Bible and prayer list in hand, next to a steaming mug of Earl Grey. Yet something momentous has occurred. I’ve left my 30s forever.

“Age isn’t a number, but an attitude,” we’re told. But the number affects the attitude. Even for those who grow old slowly and gracefully, seeming ever-younger than their years, the number doesn’t lie, and there’s no going back. The radio and television comedian Jack Benny made a living playing the role of a cheapskate whose running gag was to insist (for decades) that he was 39. I can see why 39 was a funnier choice than, say, 34 or 37. At 39, you get the benefit of holding onto a semblance of youth while living with wisdom and maturity you’ve supposedly amassed through experience.

But once you take a step forward into your 40s, there’s no going back. And frankly, it’s less like a step and more like a descending escalator. You’re going down whether you took a step or not! Youth is fleeting.

Our culture primes us to expect a midlife crisis around 40. Parties at this age are draped in black, a sign of mortality—the celebrant is “over the hill.”

I don’t share those sentiments. As for being “over the hill,” I committed Psalm 90 to memory when I turned 35, when I reached the halfway point on the way to age 70, the year marked by the psalmist as the average lifespan for “the strong.”

The biggest surprise to me at 40 is just how much faster my 30s flew by than my 20s. Some of that is due to life stage. In the past decade, we’ve seen our kids grow up. Our oldest turns 17 tomorrow and is now a senior in high school; our daughter just became a teenager; and our youngest (now with a missing front tooth) is about to be a third-grader. With kids in the house, the days are long and the years are short.

Several theories seek to explain why time speeds up as we grow older. The one that makes most sense to me focuses on each year representing a smaller percentage of life. If you are ten, a year is ten percent of your life span, and so you experience 365 days as taking longer than when you are, say, 50, and a year makes up only two percent of your life. This may explain why long car rides seem interminable when you’re a child. The trip truly does take up a longer percentage of a child’s life—in terms of perception—than it does for an adult.

(I can offer one trick for slowing down your perception of time, but it’s painful: doing planks every day. Nothing makes the minutes drag on more than adding planks to your exercise routine!)

Chesterton’s two important facts about birthdays are always timely.

First, in marking your birthday, you are affirming “defiantly, and even flamboyantly, that it is a good thing to be alive.” (Cue the Meghan Trainor song from the Peanuts movie.) Existence is better than non-existence. There is no happiness that does not begin with this simple acknowledgment.

Second, “in being glad about my birthday, I am being glad about something that I did not myself bring about.” A birthday provides a gracious reminder of our creatureliness, and the proper response is awe and gratitude to the One who has made us (and not we ourselves; see Psalm 100:3). No one chooses a birthday. The fact is, you did not make yourself; you exist because of a sovereign Creator who is the Lord of all. He defines us, not vice versa. He is ultimate, not us. He is the Creator; we are the creatures. He is self-sufficient; we are dependent. He is the source of all life; we derive our breath from him.

This transition from my 30s to 40s comes at a time when my ministry assignment is also changing. I am wrapping up my work with Lifeway and The Gospel Project, and I will soon step into a new role for developing resources at the North American Mission Board. Meanwhile, I continue to write and teach (and there are several exciting developments on those fronts I hope to share with you soon).

My annual tradition is to take a break from writing columns and posting on social media during the month of July. This year, I plan to spend a month away from even scanning social media. Cal Newport’s Digital Minimalism has challenged me regarding intentionality and tradeoffs in online connectedness.

So, dear readers, I wish you a wonderful rest of the summer and a summer of wonderful rest. Thank you for supporting me and reading my work. If you think of it, please consider my most recent books, The Multi-Directional Leader and Rethink Your Self for your summer reading stack. I pray they bless you and strengthen you in whatever ministry the Lord gives you in the days ahead. See you soon.

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