Anyone else think about how great life was "back in the day" a lot?

I'm 23 years old and I already feel like my life is over. I don't really look forward to anything. Nothing interests me. I could give a crap about socializing and am basically a hermit now. I always think about how happier life was as a child and in my teenage years. I feel totally different and unhappy. I can't concentrate on movies and am disconnected from everything around me. I see the world a lot more cynical. I get more comfortable with the idea of death as time goes on. I feel about 70 and my life is over at 23 already. I think about how people around me were happier, I wasn't so serious about life, and I felt more alive. I wish I could just go back in time and re-live those days. It's been like this for years and I reminiscence of the past more with each new year. Do you think of the past a lot too?