I just noticed that I am now 50

Last month I turned 50 years old. A lot of people turn 50. More now than ever in human history, as a matter of fact.

It's interesting to think that life expectancy for American men in 1900 was about 46 years. It is now pushing 79.

As my favorite author Bill Bryson puts it in his (excellent) new book "The Body: A Guide for Occupants," that's not because men in 1900 were turning 46 and immediately keeling over. It's because so many children died in infancy, pulling down the overall average.

Still, at the turn of the 20th century, once you hit 50, you started living on borrowed time to a very real extent. Chances were good that an infectious disease of some sort would eventually get you.

Nowadays we've conquered most of those infectious diseases. We just die of heart disease and cancer instead.

All of which is to say, while I feel blessed to live in an age when men are living to nearly 80 on average (and woman beyond that), you can't help but notice once you turn 50 that, mathematically speaking, you are very likely on the downhill side of your personal roller coaster ride through life.

How far you actually make it is largely influenced by your lifestyle choices, of course, but also by genetics. People who live to 100 and beyond usually have relatives who also lived to 100, or at least close to it.

As the saying goes, if you would live long, choose your parents well.

I should mention here that it's not like I think about dying all the time. I rarely do, actually. But the thought does cross my mind with at least a bit more frequency now than, say, when I was 30.

When you're 30, you can reasonably expect that another half century will pass and you'll still be here.

When you're 50, it feels like you're asking for a lot if you expect another 50 years. It happens, of course, and medical science is getting better all the time at extending your stay on this planet. But living to 100 often takes a very deliberate effort to live to 100.

For those who get there, it's usually because they lived in a way that was conducive to longevity.

I do some things well when it comes to personal health, while I slack on others. That's probably how most of us are.

The most powerful anti-aging factor I likely have in my corner is simply that I have a good time. I mean in general. I just really like life, and specifically the life I happen to lead.

Yeah, I complain regularly about this or that. But all things considered, I kind of hit the jackpot when it comes to personal circumstances and overall contentment.

I have it good. I'm very blessed. I enjoy myself day in and day out.

I don't yet have the kind of health issues that become common as you age. I have no chronic pain, I have no diabetes, I have no cancers of which I'm aware, my organs all function more or less pretty well, and I feel good when I get up in the morning.

That changes with time, I understand, but I run regularly, which I know helps a lot. I've let my weight creep back up lately so I have to address that, and I have a genetic predisposition toward high blood pressure that has me on a very low-dose prescription medication (at least until I get those BP numbers back down naturally, at which point I would like to ditch the lisinopril).

But taken as a whole, I'm in a pretty good physical state. I don't even (yet) need reading glasses, though like I always say, that's coming.

It is, like all things, a matter of perspective. People older than 50 would love to be 50 again, and people younger than 50 dread it. I get it, especially now that I'm transitioning from one of those groups to the other.

50 may be the new 40, but I'm not even sure what that means.

All I know is, I'm starting to have to pee a lot more than I used to. And if I have to complain about anything associated with advancing middle age, I'm going with that.