Things change as you age. You can either fear it, or embrace the journey.
I don't recall specifically anything related to my tolerance for alcohol changing around age 40 but my willingness to, shall we say, "overindulge" has declined with time. The next day is usually a loss, and I don't have time in my life to lose days to hangovers. Others may have different interests and priorities. I don't judge.
I have a regular poker game once a month w/ some buds. Started about, oh, 11 or 12 years ago. I could stay up until 2am and still be functional the next day. Beer was part of the night, but never sloppy stupid--it's not conducive to poker.
About 2 or 3 years ago, I started to realize that I tend to wake up the same time in the morning. If I got to bed at 2am, that just wasn't enough--and the next day is a loss, just like having a hangover. I now quit at midnight when we play. It's long enough.
Now, I'm a bit older than 40--I'm 58--but the message is the same for everyone: things change as you get older.
You can either fear the change or embrace the journey. The first doesn't sound that fun, but believe me, the second is much more enjoyable.
I don't have quite the stamina I once did, my lower back is a problem, I don't sleep as well as I did at one time. But you know what? There are tons of people in the cemetery that would be happy to change places with me.
You find workarounds. Ways to compensate. Alternatives. It's part of the journey--am I clever enough to find ways to still enjoy my life? Perhaps a decline in tolerance for alcohol will accompany a greater appreciation for other things, like certain beer styles.
I now have greater time and interest in learning about new things. I developed and published game theory for fantasy baseball. Learned to build golf clubs. Learned to golf passably well (shot a round of par once). Learned to play poker (not well, but I understand the theory
). Learned firearm sports and reloading. And now, I'm learning to brew beer. It's interesting, complicated, but when you hit, you really HIT!
What I was once interested in, I'm not so much any more. New interests emerge. Our bodies change. It's part of the journey.
Enjoy it!