Personally, I think we should ignore the idea that your life's theme song would be whatever was #1 on your eighteenth birthday.
I can think of a few songs that I might think were mine, and my birthday wouldn't necessarily have much to do with it.
The classic
They're Coming To Take Me Away, Ha-Ha would be near the top of the list!
But my eighteenth birthday? That would be
Brother Louie by The Stories.
Not my life theme song at all. In fact, it reminds me of a particularly unpleasant incident that happened a couple of months earlier. The less I think about it, the better.
Strange, but the more I think about it, albums come to mind. More than individual songs, for some reason. At least at this hour of the morning. And not necessarily from the exact month and year of my birthday. For now, I'll settle on
Colors of the Day - The Best of Judy Collins. Other choices would be revealing too much.
Signor V.