Read it through once

-- St. 21. He digresses here, and does not return to the subject till the 31st stanza, “What did I say?--that a small bird sings”. The path gray heads abhor: this verse and the following stanza are, with most readers, the CRUX of the poem; “gray heads” must be understood with some restriction: many gray heads, not all, abhor --gray heads who went along through their flowery youth as if it had no limit, and without insuring, in Love’s true season, the happiness of their lives beyond youth’s limit, “life’s safe hem”, which to cross without such insurance, is often fatal. And these, when they reach old age, shun retracing the path which led to the gulf wherein their youth dropped.