When you were 20 and saw the dangerous fruits of the all-heart-no-brain worldview, you were wise enough to understand that the brain must always be in control, even while listening to the heart.
But the saying is also a gentle reminder that you are NEVER too old or young for that manner to change for the better.
....And even then there are times when the head must give way to the heart, but those times must be realized as good for that to happen.
Make of that what you will...