iirc BTS were all barely 20 when debuting, with maknaeline all in middle school and highschool meaning they're 17 yrs old and below, while not as young as TXT the discrepancy isn't that huge so far
TXT actually seems to be the normal age for bg debuts rather than too young, people forget Taemin debuted at 13. In kpop, having maknaes who are 14 and 15 is more normal than the exception (look at big groups, odds are maknaes are from 14-16 years old)
Seeing their oldest is 19 years old, that instantly makes him older or same age as SHINee's eldest and the whole of DBSK during their debut. Lest people forget, DBSK's eldest is Jaejoong and he was only 17 when DBSK debuted in 2003.
I just don't get all the fetus and embryo jokes unless all members are 15 years old and below.