If your over 18, it goes by your income. Some people have to report their parents income though. If you need any help with Job Corps, heres their information from their official website:
Call (800) 733-JOBS or (800) 733-5627 where an operator will provide you with general information about Job Corps, refer you to the admissions counselor closest to where you live, and mail you an information packet.
If you want to read the information they provide about joining Job Corps, the website is: http://funadvice.com/r/14q8htoeeei
Im not exactly too sure although if your parents have high income, they could not accept you. I heard it differs in different states. Your better off calling them and asking. Their website doesnt offer too much information.
would it go by your parents income if you live with them?