middle age

Short definition from Wiktionary

Noun

1. 1
   The period of life directly preceding old age, often defined roughly as ages 45–65; midlife.

Proper noun

1. 1
   Alternative letter-case form of Middle Age.
2. 2
   Alternative form of Middle Ages.
3. 3
   Alternative letter-case form of Middle Age.

Adjective

1. 1
   Attributive form of Middle Ages.