I know this exactly. After realising that , you’re not going to live forever and you only have the allotted 70 years or so, and that you have already wasted most of it .....That is a horrible thing to deal with.
But you do. My awakening was 20 years ago. I am already past the “three score and ten” years so every day is a bonus. I am not good at keeping positive but I try. Just enjoy every day as it comes.