Regarding The renewal of Advent of the Goddess side effects for Chapter 4...

If a person hasn't started on the new quests, like say, an elf, but has started G13 before the update, will they be stuck at a standstill until G1~G3 have been completed?

Disregard this...it seems to work so far for G13...as for g14 and up...unsure.

Well it seems like if you made a character before the update, they are allow to proceed with later generations.