Look, 40 isn't easy. I know. I'm almost 6 months older, remember? You do remember, of course you do, you like to remind me that you are younger, if only by a few months. But now we are both 40 years old. It does take some time to get used to, I'll give you that. So maybe you can't stay up as late, or drink as much, or ride your bike as far, but that's not all that important, really.
What matters is who you've become: A wonderful father, a supportive husband, an accomplished professional. I like how you've softened, not physically (although I know you think this is true, I don't agree) but in your demeanor. It isn't all about rushing and stressing, getting something done. You take the time to play with the kids, listen to my stories, share our lives.
It is freeing, really, being 40. A true grown-up. Perhaps not hip, but sophisticated, wise, comfortable. You keep getting better, baby. And here's another bit of advice:
Just remember, no matter how old you are, I'll always be older.
Your old lady