Happy Birthday!
40 was a breeze for me. My better half is 3 years my senior, so whatever the number, she's always older, hehe. I hope she doesn't read this :/
As others have stated, getting older is much better than the alternative. While ever your bum is pointing down, you're doing ok.
I did think my life was over at 30 (it nearly was at 23), but I'm still rollin' around.
Enjoy It!!