“Vanity of vanities,” says the Preacher; “Vanity of vanities, all is vanity.” (Ecclesiastes 1:2)
But that is not feeling old, it’s more like wondering if there isn’t something better I could be doing. There is of course, but I can’t be bothered. That’s it.
When you get old you feel you can’t be bothered because most things don’t matter that much. Or not as much as they used to. Or not as much as they ever should have done. I just wish I had known that then when I was younger.