We can rock all day in rocking chairs of gold ...'
'There'll be time enough for sleeping when we're dead, my love
There'll be time enough for sex and drugs in Heaven'
If A Pretty Girl is Like... is a riposte to Irving Berlin's A Pretty Girl is Like a Melody", then Time Enough For Rocking When We're Old might be the answer to Bon Jovi's I'll Sleep When I'm Dead [lyrics]. There's an obvious pun on 'rocking', traditionally associated with sex and drugs and marking you out as not old, but here proposed as something to be postponed until dotage — opposed to the infinitely more immediate urge to go dancing.
A spanish duo named Espanto (www.birrayperdiz.com) covered this song in spanish.