Here’s how I know I’m getting old: More and more often, I struggle to maintain consciousness until 9 p.m.

It didn’t used to be this way. When I was a freshman in college, there was never a night – never – that I hit the hay before 1 a.m. Very often, on the weekends, there was no sleep until sunrise. There was too much life to be experienced; “I’ll sleep when I’m dead” was the prevailing attitude among my friends, an ideal lived if not spoken.

It didn’t hurt, I suppose, that I made it through my first two years of college without a single class before 10:30 a.m. And my attitude certainly changed my senior year, when I got my first newspaper job.

Still, even as I entered real adulthood, with its get-to-work-by-7:30 a.m. realities, I maintained my priorities: Sleep was a last resort. If there was fun to be had, then I needed to be there. Sometimes – not often – I would show up at work with only an hour or so under my belt.

Then I turned 30.

Bill Cosby used to do a routine in which he described the day before he turned 30: He spent all day on a basketball court with friends, playing for hours and relishing his body.

The next day, his birthday, he could only wheeze up and down the court like the old man he’d suddenly become.

I’ve never been much of a basketball player, but I could identify. Suddenly, five and six hours of sleep weren’t doing it for me anymore. It wasn’t that I couldn’t work effectively the next day on short hours; it’s that I couldn’t even stay awake long enough to have a short night’s sleep.

No more Conan O’Brien. No more Letterman. And soon, even late prime-time had become a rarity.

And I started relishing mid-day naps on the weekend. What happened to me?

Well, maybe my body is trying to keep me alive. Last week, the Los Angeles Times reported that regularly getting a good night’s sleep, about seven hours, increases your life span. Too little or too much sleep – less than five hours or more than nine – was associated with shorter lives.

“I’ll sleep when I’m dead,” it turns out, is not a philosophy: It’s self-fulfilling prophecy.

Now if you’ll excuse me, I need a siesta.