Responses
Even marriage age back then starting sooner than we know now
I bet he's around 15/16 since he said it's too early for him to retire from being a prostitute.
beta
In old Japan, there were some young boys that would be taken as apprentices or such and in return would sleep with their masters. The age range could be as young as 8 to about 19.
I don't know how young the uke is but the fact that he has been with the master for awhile means that he was definitely too young.