((a)) ** .—** Except as provided in subsection (b), if the victim of an offense under section 2261A is under the age of 18 years, the maximum imprisonment for the offense is 5 years greater than the maximum term of imprisonment otherwise provided for that offense in section 2261.
((b)) ** .—** Subsection (a) shall not apply to a person who violates section 2261A if—
((1)) the person is subject to a sentence under section 2261(b)(5); and
((2))
((A)) the person is under the age of 18 at the time the offense occurred; or
((B)) the victim of the offense is not less than 15 nor more than 17 years of age and not more than 3 years younger than the person who committed the offense at the time the offense occurred.