i think it is talking about being with a group of people who you can connect with.. for example i went to youth camp and made a lot of new friends and i wont see any of them til next year. it is about reflecting on the good times of your life.
This song is nice. i heard it on the radio today, and was surprised to find that it's green day. green day is so much more... rock... and emoish. this sounds cool. I wouldn't be surprised if this weren't edited by synthesizers or anything.
I belive this song is about every single person that has heard it becuase we have all had our ups and downs and in the end we all hope we had the time of our life.