Im happy to assure you from my own experiences, that you probably aren't going to be at the same level of intellect or mental processing forever.
At exactly around your age I felt the same. Id taken up Tai Chi and really gotten deeply into the philosophy behind it. And I felt that even at the age of 21 I had begun too late to achieve all the things and explore all the possibilities that that martial art had to offer.
I felt even if I lived to be 1000, I would never be able to get where I wanted.
This seemed to cross over into other things in my life at the time too, and I came up with the concept: The more I know, the more I realise just how little I know.
I became aware for the first time; there is just so much out there in the world, that one human being in one lifetime just cannot get it all in. You cannot experience everything. You cannot learn everything. You cannot theorise and philosophise and know everything.
I actually wonder if we as humans aren't experiencing and learning all these things separately so that it can all be assimilated into some eternal ethereal higher consciousness.
Maybe that is the mind of God, who sees all and knows all...
And all our lives and our thoughts and experiences and decisions aren't the universal equivalent of neurons firing in a brain.
(I feel there is more to that idea, which Im working on. Someone remind me to write more on that theory. See, there is just so much to think and learn and know and work out.
But you can be assured that your level of intelect should change if you are a thinking person.
I myself, at your age could not have come to this site and held the same conversations I do now. I was intelligent for my age, but just no where near what you younger guys are.
I have changed so much from the way I thought in my early twenties to become the kind of thinker I am now.
It is also one of the things that gives me hope for the future. That each generation learns things faster and becomes just that little bit more sophisticated.
And this is what you have to accept. You will never have all the answers. But you can learn and experience what you can in your lifetime and pass it on. And those that come after you (the ones that actually think.) will be saying what you are saying- but maybe at the age of 15, instead 23.