Yeh I know that feeling.
It makes you start thinking about where the years have gone. What you have accomplised in your life, and what is left that you should do.
The way I start looking at things is well lets see I probably have 25 good years left to live.
Good health is the key thing and I have some health issues to deal with in the coming years.
The other thing I think about is if I could be 31 again , would I ? And take years back that I have lived ? Not sure that would be a good idea.
oh well .
Life is pretty much a bitch, and then you die.