Well... I typically avoid replying to posts in the Men-Focused Support forum. But I noticed you had yet to receive replies to this post. So I thought I would write one.
I'm 71 years old now. But I often have to remind myself I'm not 21 anymore. (My body does help with this though by keeping me aware of just how old I really am.)
I recall my father saying, one time many years ago when he was younger than I am now, that he didn't feel any different "inside" (probably in his 60's) than he did when he was young. So I tend to think that, while we age on the outside, mentally we don't change that much as the decades roll by.
There is this thing that tends to happen in middle age, though, that is referred to as the "mid-life crisis" where men especially begin to feel the urge make dramatic changes in their lives. Perhaps that is some part of what you are experiencing? Here are links to 2 articles, from PC's archives, on the subject:
The Male Midlife Crisis
When Men Feel Trapped: A Practical Guide
For me, it was around the age of 50 that the wheels started coming off my cart, so to speak. They've been wobbling off & on again ever since. So I don't think I could say that my mind seemed sharper in my early 50's than it was when I was younger. I guess I was, perhaps, more "settled" & in some ways more mature. But it was also the point where inner conflicts I had kept buried all my life began to get the better of me. The result was 2 major suicide attempts one around the age of 50, the second around the age of 60. (I seem to be on something of a 10 year cycle.)
I always assumed, I guess, that the inner conflicts I kept buried all of my life would gradually resolve themselves as I got older. But what has occurred instead is that I've just gotten crazier. So I always like to encourage younger folks to do what they can to resolve their mental-health issues while they're young because, for one thing, the older you get the less the mental-health services system cares about your problems. And for another (at least based on my own experiences) you don't get saner with age... you just get weirder.