Do not think about all the time you have wasted. Think about all the time you have and what would you want to do with it.
The only destination any living creature has is its death. So, never think that its over. We have a lot of time, and we can do many things to amaze ourselves. 
When you feel lifeless, down and stuck with something. Just put some loud music, a song in which the vocalist growls his lungs out. Start doing some fucking thing. And you will be on track.
My random thoughts.