It's in New York,he brings his lunch to school,I'm not sure how he gets to school but I hope this info helps.
In NY, if you are 14 or 15 and school is
not in session, you are permitted to work up to 8 hours per day, 40 hours per week and have to abide by curfew laws (7am-9pm) and can only be employed between June 21st and Labor Day. When school is
in session, hours are only permitted outside of school (obviously) and between 7am-7pm for a total of 3 hours on a school day and 8 hours on a non-school day, with no more than 18 hours per week. 18 hours a week is next to nothing, unless he is getting paid $100/hour, which is
extremely unlikely there is no way he can be making 'big bucks'. These are all based off of the state level Child Labor Laws for New York and do not cite Federal Law in this, since State Law will suffice for your argument to your friends.
To cite some specific information that is relevant to your current case;
"Minors 14 and 15 years old may work after school hours and during vacations, but not in factory work. They may do delivery and clerical work in any enclosed office of a factory, and in dry cleaning, tailor, shoe repair, and similar service stores."
"There is no minimum age for child performers at theatrical, radio, or television performances or for child models."
Luckily for you, I don't think the manga industry (which is based entirely in Japan?!--Unless you are referring to translations which most tend to be FAN translations, done for FREE) is not the physical entertainment business.
"Minors 11 years of age or older may work outside school hours as newspaper carriers to deliver, or sell and deliver newspapers, shopping papers, or periodicals to homes or business places. Minors 14 years of age and older may be engaged in street trades work, i.e. selling newspapers or periodicals on streets or public places.*
*(Under Federal law a 14 year age minimum is required for delivery of periodicals and similar items.)"
Perhaps he sells manga on the street and therefore has a 'claim' in the manga industy? Lol?
(Source: http://www.labor.state.ny.us/workerprotection/laborstandards/workprot/schlattd.shtm)
Lastly, FM--was this kid a nobody before he opened his yapper and claimed to be a super manga business man? Obviously he is doing this for friendship and companionship during school hours. Perhaps his home situation is rather sad and he needs some friends to cheer him up at school so he constructed this lie to appear much cooler than he is, so he is living out this fantasy of who he wants to be rather than who he really is? Just saying, try to see his point of view in this rather than just demolishing him with facts that he is lying. :3!