1. No one in their early 40s can believe they are in their early 40s.
    No one. Not a one.
  2. You catch yourself thinking about your 20s like it was two years ago.
  3. You think about dying a lot more.
    Sorry, it's macabre but true. Web MD was always a little terrifying but now it is a hellhole that you can slip down for hours if you're not careful.
  4. You have more stability than you ever had before in your life.
  5. On the other hand, parents at your kids' school are all starting to split up. So....
  6. You really do give less of a shit about all of the shit you cared about when you were younger.
    Including: impressing people you don't know and wearing uncomfortable but beautiful clothes.
  7. You are kinder to your parents.
    They're older now, and also, your kids have proven what hard work it was to raise you.
  8. You stare in the mirror from a lot of different angles and still don't think you look 40.
  9. You say things like: "Oh, I don't know...you're much younger than I am," and people used to protest that you are the same age...but they don't protest much anymore.
    Like yesterday when I said that to the salesgirl in Scoop when she suggested I wear a really cute lacy bra that could be fully seen under a shirt. Me: "oh, you could pull that off. But I'm much older than you, I don't know." Her: "Well, you could just wear a tank top." Sigh.
  10. You finally wear sunscreen and floss daily.
  11. You make choices based on the thought of: "fuck it, I'm in my 40s."
    Meaning, you apologize less and are more autonomous. This train of thought gave me the courage to go indie on my last book, which was the most gratifying professional experience I've had since book #2.
  12. Going out late, say, after midnight is a collective worst nightmare.
    I turn into a pumpkin at 11:30.
  13. It's better than you thought it would be.
  14. You realize people make mistakes - sometimes really big ones- but that doesn't make them unforgivable or irredeemable.
  15. One night of bad sleep and you could be mistaken for an extra on The Walking Dead.
  16. Seriously, what the fuck? How am I 42?
  17. You find yourself doing the thing where you are surprised that a 20-something doesn't know something that is a huge cultural memory for you
    Like: srsly, you don't know who Phil Donahue is??
    Suggested by @ChrisK
  18. You sometimes still check the demographic box that says 25-39.
    Hey, don't judge.
  19. You get carded and the bouncer says, "Whoa. I didn't know you were THAT old."
    Suggested by @EricElkins
  20. When you're in a bar and see the sign that says "You can drink if you were born after June 29, 1994" you feel...a little droopy.
    Suggested by @ChrisK