If all the world and love were young,And truth in every Shepherd's tongueThese pretty pleasures might me move (1-3)
The use of the phrase "pretty pleasures" drips with condescension. It's obvious from the start that the nymph thinks the shepherd's offer is sillier than these cats. And, man, those cats are pretty silly.
A honey tongue, a heart of gall,Is fancy's spring, but sorrow's fall. (11-12)
Speaking in proverbs is one way to insure you never end up sounding foolish. Right?
In folly ripe, in reason rotten. (16)
In this line, foolishness and the life of springtime are knotted together. So, be careful driving from March to May.