You are not currently criminally guilty of incest according to statute. Your brother meets one part of the statute, but as you are under 16, does not appear to be in violation yet. I suggest you both prepare to deal with the ramifications and take appropriate measures before you reach 16.
§ 5-26-202. Incest
(a) A person commits incest if, being sixteen (16) years of age
or older, he purports to marry, has sexual intercourse with,
or engages in deviate sexual activity with a person he knows
to be:
(1) An ancestor or a descendant; or
(2) A stepchild or adopted child; or
(3) A brother or sister of the whole or half blood; or
(4) An uncle, aunt, nephew, or niece; or
(5) A stepgrandchild or adopted grandchild.

