Don't feel lonely! I'm another teenage Bowie fan, and I've had to suffer persecution (well, light teasing) for it!
Anyway, if I remember correctly, I believe "Five Years" is about a young man coming to grips with the end of the world (we only have five years left to live, hence the song's title).
Take a look at these lyrics if you don't believe me:
"News had just come over, we had five years left to cry in
News guy wept and told us, earth was really dying
Cried so much his face was wet, then i knew he was not lying"
The "narrator" of the song prepares for the end by cramming his hea