Tonya is obsessing about turning 40 and soliciting advice from people who have. So I'll respond.
When you turn 40 (or any of the other 0s), you can finally stop thinking about how you're about to turn 40. You just did. It's the lead-up that's the problem. And it starts early, maybe even on the "5." That is, you've been thinking, oh no, I'm pushing 40. You don't have to think that anymore, and it's at least 5 years too early to start with I'm pushing 50. It's only the pushing that is onerous. No one ever frets about pulling 40. There isn't even an expression "I'm pulling 40." That's because the 0s are only hard to push, not to pull. So just get around over into the pull position and it'll be just fine. So enjoy the next 5 years. In fact, enjoy the next 8 years: you're free to see years 44-47 as your "mid-40s." Don't go with the "pushing 50" thought until you're 48. And then, you have my sympathies, because that's really going to hurt.
Which leads me to my second point. You can feel much better right now if you just think how it would feel if you were turning 50. But what about these poor souls who are pushing 50? Well, they can just think about how people turning 60 feel. But really, once you're 50, you've thought too much already about the subject, and, like a lot of other things, it's become too boring to keep thinking about. In fact, one of the benefits of being over 50 is that a lot of formerly troubling thoughts just don't have the power to bother you anymore. It's quite liberating to be so jaded.
UPDATE: Prof. Yin has a way to lengthen the time between the aging obsessions. I think if the zeroes came up more frequently we would make less of them. If the time between zeroes were longer, wouldn't we really flip out when they came up? Or is 10 years exactly the time period that makes the zero seem so significant? I remember turning 10 and thinking it was tragic that I would never again be able to write my age with a single digit. And that I was one-tenth of the way toward being 100. And how horrible it was to think that I was probably at best only going to have 9 more stretches of time equivalent to the inconsequential time period I'd already lived. I found that quite frightening, and I did not even yet realize that the 10 year periods feel much faster when you are older. I thought 10 years when you are a child seem like very little because when you are a child you hardly get to do anything. A related tangent: someone was saying recently that if the words "eleven" and "twelve" had been "oneteen" and "twoteen," we would not have the notion we do of what a teenager is.