We tend to divide humanity into segments. By nationality, ethnicity, gender …

A grouping that some people don’t always think of quite as readily:

Groupings by age.

And I now root for old guys. Because I am one and because I understand far better the challenges they face.

That’s why I’m a bigger fan of Tom Watson right this minute than I ever was during his heyday. Or at least his first heyday.

Watson is 18 holes away from winning the British Open — at age 59! Which would make him the oldest winner of a major. By 12 years.

Watson is 4-under after 54 holes at Turnberry, where he won a British Open once before. In 1977.

I had to laugh, today, when some guy hosting on ESPN News actually said, “Remember the Duel in the Sun” that Watson had with Jack Nicklaus at Turnberry in 1977? … and I’m pretty sure that particular glib ESPN talking head wasn’t older than, say, 5 years old in 1977 and I rather doubt he was watching golf. At age 5. Or age 1.

Anyway, yes, I root for old guys. I always have kept fairly close track of athletes older than I am. Which was everyone important, until Chris Evert came along. (She made me feel like a failure, because she was winning tennis tournaments at 16 and I was 17.)

I made a point of noting how many guys were older than me in the majors, when the crowd began to thin. I know that one of the last ballplayers older than me was Dave Winfield, who was 43 when he played his final season, in 1995. There might have been one or two other lesser guys.

So, yeah, it’s been a long time since someone who predates me was doing anything important in sports (aside from the Senior Tour) … so this is pretty exciting for me.

And it’s great for all of us AARP members. Or at least, potential AARP members.

It’s not easy to win a sports event when you’re 45. Never mind 50, 55 or 59.

Not even in golf. Though it is the only major sport I can imagine where it would be even possible.

Golf doesn’t require explosive speed or strength, or massive stamina. Not to say it’s a walk in the park. If I put in 6-7 miles for 4-5 straight days, it would start to get to me. If I swung a golf club as hard as I could for that many days straight, I’d probably strain/pull/tear something.

But what really gets to aging golfers, I think, is what all the years do to the nervous system.

In golf, the first thing to go is the ability to make putts. The condition is known, historically, as “the yips.” A sort of failure of nerve when standing over a big putt.

It’s not possible to relate to this, when you’re young. When you’re young, you ascribe this whole “yips” thing to some sort of mental weakness. More a matter of will than anything else.

But having chased Watson into near old age … I can tell you that your nerves do fray as you age. And they come unraveled much more quickly, and are triggered far more easily.

The freeway commute that used to be fun or at least challenging? Now one long bout of “what could go wrong next?” And those panic stops really do involve panic. Loud noises, surprises of any sort. Aging people don’t like them.

The idea of engaging your nervous system — for fun — pretty much disappears. You are not going to see people 50 and older at horror movies, thinking it’s so fun to be scared. You won’t see people 59 years old riding roller coasters.

And that’s for a good reason. Your nerves, at that age, tell you it’s a bad idea. To have your whole body infused with adrenaline, to jump into action like that … you discover it’s something you don’t like and tend to avoid, if possible. It doesn’t excite you; it makes you feel rather ill, actually.

So, now we have One of Us with a chance to win the British Open. Playing in front of huge crowds, and TV cameras, against the best golfers in the world, trying to make history under enormous pressure.

I would love to see Tom Watson win. Because he’s a nice guy. Because it’s a great story. But mostly just to reassure me that, yes, it is possible for someone older than me to thrive in a massively pressurized sports situation.

I have a hunch Tom Watson is going to melt today. I know what it’s like to be 55, and I doubt I could keep my nerve. I’m sure Watson is made of sterner stuff, but to beat a field of guys barely half his age …

I fear he will melt. I really hope he doesn’t.