This. Although it predates me by 30 years, still, it's a song from my youth, once a nice melody, but with the passage of time, the lyrics have meaning for me now that wasn't there when I was younger. 

Across the evening sky,
all the birds are leaving,
But how can they know,
it's time for them to go?
Before the winter fire,
I will still be dreaming,
I have no thought of time.

For who knows,
where the time goes?
Who knows,
where the time goes?

Sad, deserted shore,
your fickle friends are leaving,
Ah, but then you know,
it's time for them to go,
But I will still be here,
I have no thought of leaving,
I do not count the time.

For who knows,
where the time goes?
Who knows,
where the time goes?

And I am not alone,
while my love is near me,
I know it will be so,
until it's time to go,
So come the storms of winter,
and then the birds in spring again,
I have no fear of time.

For who knows,
how my love grows?
And who knows,
where the time goes?

I had to google that - 

It's the inevitable passage of time, I think, which isn't so apparent when you're younger. 

Time is something I've thought about a lot.

It's the inevitable passage of time, I think, which isn't so apparent when you're younger. 

Time is something I've thought about a lot.