That time of year thou mayst in me behold
When yellow leaves, or none, or few, do hang
Upon those boughs which shake against the cold,
Bare ruined choirs, where late the sweet birds sang.
In me thou see'st the twilight of such day
As after sunset fadeth in the west;
Which by and by black night doth take away,
The “ruins” may be a place where the birds once sang in warmer seasons.  The “sweet birds” are clearly a  metaphor  for youth, and the time of singing suggests life and freshness. 
 The two images — ruins and choirs — may seem mutually exclusive, and yet both are drawn into the poem without conflicting with one another. 
 The image of the ruins, however, raises a question of why the young singers are occupying ruins — this can’t be a reference to the time of year as ruins are ruins at any time.  However, the image does fit the quatrain in terms of its similarities to “old age” and its concrete connection to the branches shaking against it. Just as once a new, “young” building existed, they are now breaking down and unusable, just as the human body breaks down and becomes disabled. 
 Source: Spriester, Brett E (AKA  Maximus ). “Wanted.” 2012.
Sonnet 73