Too Old by Andromeda (a largely-forgotten proto-prog band from 1967/8, the precursor to Atomic Rooster):
It's time to think about the time when you grow old
And to think about the times that you've been told
Of what to do when years they seem to hurry by
Got to face the facts, it does no good to lie
The years pass on
And before long
There's nothing left for you to do, the time has gone
You've got to think of all the things you planned to do
And of all the places you were going to
You've had your chance and now it's too late, the days are past
You should have (made?*) it while you had the chance
Just live today
Not years away
And take no notice what the people [undecipherable] say.
(*I couldn't quite hear what this word is; I've typed my best guess.)
I found this quite a haunting song when I was 15; even more so 40 years on.