noun
prime of youth; bloom of youth
Refers to the peak period of youth, full of energy and vitality. Often used in literary or slightly formal contexts.
彼は若盛りで、毎日スポーツに励んでいる。
He is in the prime of his youth and devotes himself to sports every day.
若盛りのエネルギーを仕事に注ぎ込んだ。
I poured the energy of my youth into my work.
Compound of 若 (waka, 'young') and 盛り (sakari, 'peak, prime'), with rendaku voicing of 盛り to ざかり.