One's Lifetime
One's Career
noun
A life horizon is your life, which you're looking out over, all the way to the very end. This is one's lifetime, though it could also refer to one's career. Basically, at the end of it something dies.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
生涯ずっと独身なんて嫌だよう。
I don’t want to stay single my whole life.