I turn 40 next week. “Over the hill” as they say. For someone who had their first existential crisis at age 5, a milestone like this is huge. Bigger than I want it to be. But with age comes wisdom, and my angst has definitely mellowed.

25 hit me like a freight train. Fortunately I was not literally hit by a freight train, as that is just the kind of untimely end I have long feared most. But I was not expecting turning 25 to trigger the kind of fear and dread I had first felt on a dark night when the raspy voice of death first whispered in my ear as a kindergartener, and had not really felt that much since.

For several months after I turned 25 I felt traumatized by death’s unwelcome return. Eventually I began to develop a new perspective on mortality, and I was at peace with the finiteness of my existence for another 15 years.

But now as 40 approaches I once again find myself lying awake in bed at night, staring into the darkness, grasping in the darkness, feeling each second slip past, gone forever, one fewer remaining between this moment and the last.

As I said, my angst has mellowed. It’s not what it was 15 or 35 years ago. But what it lacks in harshness it makes up for in urgency. It used to be easy to look ahead into the vast distance of my life, recognize that the end was out there… somewhere… and fear it but still feel somehow immortal. (“Learning that we’re only immortal for a limited time,” as Neil Peart wrote in the lyrics to the Rush song “Dreamline.”) But now it feels — it is — closer, more imminent.

The average male life expectancy in the United States is 78 years, which means that, statistically speaking, I’m probably more than halfway to the end. Under the best of circumstances I may live more than another 40 years, but I might suffer disease or infirmity for a large portion of that time. Or, I might die in an accident or of a disease at some point within the next 20 to 30 years. I might die tomorrow. That’s always been true, of course, and in some ways I suppose your chance of dying in an accidental death probably bottoms out around 40 — you’re old enough to avoid Darwin Awards-style poor choices, but young enough to still have your wits and your agility.

The biggest thing I am starting to learn as I approach 40 that is helping me cope with this kind of existential downward spiral is a growing understanding of selflessness. I have always been pretty self-centered, I can admit. But when you’ve lived for four decades you do start, a little bit, to see an arc of time greater than the span of your own existence. (Or, if you’re not a selfish jerk like I am, you’ve probably seen things that way for a long time.) You finally start to really get that it’s not all about you, that you’re lucky to have the time you have, and then you just need to get out of the way for the next generation.

Which doesn’t mean I don’t want to relish every moment I have before they’re gone.