Time creeps up on us all. I think the older you are when you realise it, the more worrying it is because when one feels like it has 'caught' you up by surprise, you evaluate your time and you inevitably feel like you could have done 'more' with it or that you should have started realising it much sooner, perhaps in a way which you could have done something about it. But I think this is a self defeating loop: You never can remember/evaluate/appreciate all the things you did/experience in your life.
I think the past's details are faded, and have made way for the newer details in life and it's only now that one searches for the past details to help evaluate ones entirety, that you realise it's not easy to evaluate those past experiences because they aren't aren't as easy to experience/recall again and I think it's this dilemma that makes us feel incorrectly that we just 'existed' and not 'lived' during these times .
In truth I suspect that we did truly 'live' and like then, we live 'now' - only difference is we remember so much better now. So try not to evaluate your entire life on the long faded details of the past - sure appreciate they were once lived, but rather evaluate life now by being present and awake.
I feel this way about my early life, I long to recall detail about my childhood that I know I enjoyed but can't remember. Same goes for growing up between ages say 10 to 14. Or how I truly felt as a primary school kid, or what I was thinking about while playing in the veld - to me they don't have any detail - it just feels like I 'existed' but I didn't I lived.
I don't even remember details about weekends spent with friends...