Almost 50 here. 40+ is not just an age. It sucks being in your 40s. Things really don't work the same. My brain is slower, I get confused a little bit more, I struggle to find the right words at least 3 times a day. Even worse, your parents get sick and you have to start worrying about them and taking care of them.
Enjoy your 30s to the fullest, because it gets worse and it's completely out of your control to make it better. The best you can expect in your 40s is to slow down the decline.