Never.

There are gains for all our losses 
There are balms for all our pain; 
But when youth, the dream, departs 
It takes something from our hearts, 
And it never comes again. 

We are stronger, and are better, 
Under manhood’s sterner reign; 
Still we feel that something sweet 
Following youth, with flying feet, 
And will never come again. 

Something beautiful is vanished, 
And we sigh for it in vain; 
We behold it everywhere, 
On the earth, and in the air, 
But it never comes again.

Richard Henry Stoddard