"Must be rare in this age of life" is actually "Must be aware of this age-old plight"
In my humble opinion, this song is about wanting to be in love and wanting to find that someone to share your life with, but being unwilling to settle for just anyone. And maybe about feeling pressured to find someone and settle down simply because its what you're expected to do at a certain age and its what everyone around you is doing. Hence "But this is a song about feeling left out / And this is a song about not being ready / To do what you've been told to do"
"Must be rare in this age of life" is actually "Must be aware of this age-old plight"
In my humble opinion, this song is about wanting to be in love and wanting to find that someone to share your life with, but being unwilling to settle for just anyone. And maybe about feeling pressured to find someone and settle down simply because its what you're expected to do at a certain age and its what everyone around you is doing. Hence "But this is a song about feeling left out / And this is a song about not being ready / To do what you've been told to do"