noun which may take the genitive case particle 'no', noun
past middle age; nearing old age; near-elderly
Refers to the stage of life when one begins to feel the approach of old age, typically around the 40s to early 60s. Often used in formal or written contexts.
He is a man past middle age, but he is very energetic.
An elderly couple nearing old age was taking a walk in the park.
age 40 (original meaning)
Historically, 初老 referred specifically to the age of 40. This usage is now rare and mainly found in classical or explanatory contexts.
In the past, 初老 was a term that referred to the age of 40.
A man past middle age was sitting on a bench in the park.
He's recently begun to feel that he's approaching that near-elderly stage of life.
熟年 describes a mature, experienced stage of adulthood with a positive tone, whereas 初老 emphasizes the onset of aging, often with a slightly wistful nuance.
老年 refers to old age itself (typically 65+), a later stage than 初老, which describes the transitional period leading up to it.
Compound of 初 (first, beginning) and 老 (old age). Originally denoted the age of 40, considered the start of old age in classical Japanese thought. Modern usage has shifted to a broader sense of 'past middle age'.