If you're not feeling depressed right now, here's something that'll help. It's easy! All you do is figure out exactly how old you are in days (Excel can help here). From that number, figure out the date exactly half your life ago. (For me, it's Sept 9, 1986.) Head over to Wikipedia, and see which song was #1 that week.
Half my life ago this week, "Venus" by Bananarama was the #1 song in the US. Now that's depressing.