noun
age fifty; one's fifties
Refers to the age of fifty or the decade of one's fifties. Often used in literary or formal contexts.
彼は五十路を迎えた。
He reached the age of fifty.
五十路の坂を越えると、体力の衰えを感じる。
Once you pass the hill of your fifties, you feel your physical strength decline.
From 五十 (いそ, 'fifty') + 路 (じ, 'road' or 'path'), literally 'the road of fifty', a poetic way to refer to the age of fifty.