[Randrak42]

Originally Posted by galdr

Spoiler for Age and Terra ending:

Actually, I am positive Kotori & co is supposed to be 14/15 years old by the time Kotaro return from frontlines. It was mentioned in the epilogue the Kotarou tree able to grew big in just 3 years.
The sprites are just laziness. Esaka should've white hair since he only 2/3 years younger compared to main route.

Spoiler for Terra:

Also, in the Memories section it's written that Kotarou is 10 years older than than Kotori and Akane (he even says "Yay, young wife!").