That's the most adorable "WHAT THE FUCK?!" I've ever seen.
Kaf starts at 14 and already amazing even back then, so does tuki who turns 17 recently. Of course we can't forget the powerhouse of today Ado as well who scream her way to stardom when she is very young. As long as they are not overworked its fine, I mean in the series we have Michiru as an example.This chapter was a subtle reminder that the idol industry can be... pretty harsh.
The real implications that Tsumugu wants to push herself and potentially destroy her health so she can get a singing voice to compete is something. Doesn't help that the mangaka loves to draw them looking super young even though they're 14 and 15.
...
Alright girls come back in 4 years after leveling up! I'm sure you'll be real power houses by then.