Collocations for middle age - noun

early
late
a woman of late middle age

approach
a bald man approaching middle age

enter, hit, reach

spread (humorous)

during middle age
possible causes of weight gain during middle age

in middle age
He mellowed in middle age.

through middle age (AmE)
from early adulthood through middle age to retirement

well into middle age
She had her first child well into middle age.