WordNet sense 1 (the period of greatest prosperity or productivity):

blossom, efflorescence, flower, flush, heyday, peak, prime

WordNet sense 2 (the best time of youth):

bloom of youth, salad days

WordNet sense 3 (a rosy color (especially in the cheeks) taken as a sign of good health):

blush, rosiness

WordNet sense 4 (the organic process of bearing flowers):

blooming