Wow, this thread made me swing between suicidal thoughts and hope.
We seem to have a lot in common. My story is set in roughly the same period (roughly, because the setting is Meiji-period Japan). My MC sounds like a poor relative of your MC – he's a servant in a brothel, a small-time criminal, and other morally questionable things. He's also highly sexually active, and to him sex is first and foremost a currency, a means to an end. And he is underage.
I don't know what to do about this, or rather if I should do anything, because the story wouldn't work if he were 18 or 19. It's a purely historical novel of Tokyo underworld in the 1880s, set mostly in various red-light districts and other seedy places, and I cannot ignore the realities of the time. Sex workers, if they were born or sold into the trade as children, began their apprenticeship very early, and started to take clients when they were between 13 and 14 years old. In Meiji period the age was raised to 16, but that was in licensed quarters. Unlicensed sex work was a different world altogether.
It's not a YA story, so I don't feel that I need to state the age of my MC. He lies a lot and tells different things to different people, depending on what he thinks they want to hear. He's not an orphan, but no one in his family cares enough to remember the exact year when he was born. When he's arrested, he just gives the police a random number off the top of his head. In Japan, you have to be entered into a family register to be a citizen, but his family couldn't be bothered, and so in the eyes of the law he doesn't exist, and the police have no choice but to believe him. The underlying meaning of this is that no one gives a shit – this lack of info is in itself a part of the story.
Various people, including some lovely AW folks, have read the excerpts, and so far my MC's age hasn't been an issue... I have just posted a nearly-sex scene in SYW and – actually, I have a lot of erotic elements throughout the book (because the MC is also the narrator) and so far, no one objected. I read your opening in the SFF subforum, and I think it's fine