I don't know. I guess these things are never really precise, so i may have made a sweeping generalization. Sorry.
I was thinking her foil relation with Houshou, a saintly mother figure, combined with her small childish appearance and youthful behavior would imply she is young, or at least of an age where revealing you have a D cup would be shocking.
She could be an unfortunate early bloomer, kind of like my sister, who struggled with bursting chest sizes as early as 13. Or, she could just be really petite, and that's the end of it.
And then, after one month, the answer is obvious. She's old enough to own a house.
open...'aighhmlgl...Because there's space there.My stomach's caterwauling! Go purrepare some food!Oh yeaaaah...roll...FWOIP!whippy
whappyShe woke up.Morning