代

(one acting as a) foster parent

to be handed down from generation to generation

trend of the times; way things are going

Proverb

you can't make an omelet without breaking eggs; a small sacrifice may be necessary to solve a more pressing problem

ancient civilization; ancient civilisation

one's youth; one's youthful days (years); the flower of one's youth; the springtime of one's life

Dark Ages

dark age

to replace; to change (for a new one); to renew

Business

to reassign (an expense); to charge (to a different account); to shift (a loss)

to change clothes (on someone else, e.g. child, doll); to change the wallpaper or skin (of a smart phone, etc.)

Biology

alternation of generations; heterogenesis

change of generations; emergence of a new generation

premodern; old-fashioned; outmoded; antiquated

Yojijukugo; Noun or participle which takes the aux. verb suru; Intransitive verb

renewal; replacement; regeneration; rejuvenation

metabolism

war by proxy; proxy war

ancient script; ancient character; ancient alphabet

by turns

taxi fare

to look old-fashioned; to be antique-looking

(one's) youth; one's younger days

child of the times; modern kid; kids of today; with-it youngster

to supplant; to supersede; to replace; to take the place of

advertising agency; advertising firm; advertising company

golden age

representative director; managing director; president; someone chosen by the board of directors from among the directors to actually represent the company in its dealings with the outside world

present-day science; modern science