Quitting on life because I don’t understand anything

I have stopped working on my life for a really long time now and everyday I wake up feeling mentally stressed and defeated before doing anything. It seems like my thoughts constantly bring me down. I see so many people younger or older improving their life whether it’s fitness, financially, in relationship. And I keep telling myself it’s too late now. Your are simply too behind in life based on your age. And I’m just tired of living this way.