1) Fifties 2) Letter 3 of our mystery guest 3) Part of a life 4) Pre-golden years time 5) Start of a bob hope quip 6) Time for a crisis 
Middle age is the period of age beyond young adulthood but before the onset of old age. Various attempts have been made to define this age, which is around the third quarter of the average life span of human beings. ==Definitions== According to Collins Dictionary, this is `... usually considered to occur approximately between the ages of 40 and 6....
• Of or pertaining to the Middle Ages; mediaeval.
period of human adulthood that immediately precedes the onset of old age. Though the age period that defines middle age is somewhat arbitrary, ... [1 related articles]
Mid'dle-age` [ Middle + age . Confer Mediæval .] Of or pertaining to the Middle Ages; mediæval. 
[n] - the time of life between youth and old age (e.g., between 40 and 60 years of age)
noun the time of life between youth and old age (e.g., between 40 and 60 years of age)