This is not original because everyone and their dog had it for their grad song, but it is called:
"Forever Young" by Alphaville
A one hit wonder, but still a pretty good song.
Also, "Together You and me" by The Lighthouse Family (not sure if that's the title or not)....
My senior year in HS, the big song for graduation was "Time of Your Life" by Green Day
Our class song was the one from Casper...can't remember the name of it...
The Eve6 song can be really easily applied to the end of school (just thinking about leaving college makes me all teary and I hear that song in my head) but its actually about a one-night stand. But the way they did the video, it makes it seem so different.