OK, I'm trying to understand something...MC mentioned he just finished school as he was heading out to live with his mom for the first time (I'm guessing he just finished high school?). Which means he's only 18 years old, and his young looks back that up.
And, so I'm guessing MC's little sister would be younger that 18...and judging by her real young looking body, she could be around 13-17 years old. (And I guess for legal reasons, she was set at 18...but it's still odd she was set at the same age as the MC, if MC just finished attending high school.)
Well, I'm going back to the story to know more...bye.