In his own words
Sonnet 73
That time of year thou mayst in me beholdWhen yellow leaves, or none, or few, do hangUpon those boughs which shake against the cold,Bare ruin’d choirs, where late the sweet birds sang.In me thou see’st the twilight of such dayAs after sunset fadeth in the west;Which by and by black night doth take away,Death’s second self, that seals up all in rest.In me thou see’st the glowing of such fire,That on the ashes of his youth doth lie,As the death-bed, whereon it must expire,Consum’d with that which it was nourish’d by. This thou perceiv’st, which makes thy love more strong, To love that well, which thou must leave ere long.
Three images for growing old: bare autumn branches, fading twilight, a fire down to its embers. Then a quiet last line about loving well what you must leave.