the prime of youth; the springtime of life
A poetic or literary expression likening the best years of one's life to spring. Often used in reflective or congratulatory contexts.
He is now truly enjoying the prime of his life.
Youth is also called the springtime of life.
A metaphorical compound of 人生 (life) and 春 (spring), directly translating to 'the spring of life'. The exact origin is uncertain, but it follows a common cross-cultural metaphor of spring representing youth and vitality.