D defs.my
Entry 1 sense Webster, 1913

Middle-aged

/mĭd'-əl-āgdˌ/ · Mid·dle-aged · IPA /ˌmɪdl̩ˈeɪd͡ʒd/
01 a. Being about the middle of the ordinary age of man; early in the century, it was considered between 30 and 50 years old, but by the end of …
  1. 1.
    Being about the middle of the ordinary age of man; early in the century, it was considered between 30 and 50 years old, but by the end of the 19th centruy it was considered as 40 to 60.