noun
half a lifetime; one's life so far
Refers to a long period of one's life, often with a reflective or narrative tone. Can mean roughly half of one's expected lifespan or the years lived up to the present.
彼は半生をかけてこの研究を完成させた。
He spent half his life completing this research.
半生を振り返って、
Looking back on my life so far, I can say I have no regrets.