Add me to the "turning 40" club.
Back when I turned 35 I went through a bout of depression. I had just had a baby and the realization hit that I was no longer the generational focus. I had sired my replacement, which woke me up to my own mortality. Around the same time I had a couple of people I knew die unexpectedly, and that just compounded the fear. It was a rough few months.
However, the baby (and eventually, the second baby) really prodded me to get in shape for once in my life and take control. It's been a long process, but the road from 35 to 40 has seen me start running, lose 20 pounds, get off my cholesterol meds, start a new job and get a promotion....all very positive lifestyle changes. I had a goal 2 years ago when this process was really starting to gel that I wanted to hit 40 in my prime. So far I'm on track to reach that goal.
I refuse to go back to that negative place I was in. 40 will be awesome. 40 will be the checkered flag for the race I've been running the last 5 years.
In that same vein, I also vowed when I turned 39 that my year to 40 would be filled with good times, great memories, family, and friends. The entire last year of my 30s will be a year of celebration. I will not say no to opportunities. I will not talk about things, I will do them. I won't need a big 40th celebration because my birthday is going to last for a year.
Love your idea ATB of flipping your celebration around. That's awesome.