youth under subsection (x)(2)(B), in an amount determined by the Secretary, but only if the agency waives for such eligible youth receiving assistance any residency requirement that it has otherwise established pursuant to subsection (r)(1)(B)(i). . 4. Exceptions to limitations for project-based voucher assistance (a) Percentage limitation The first sentence of clause (ii) of section 8(o)(13)(B) of the United States Housing Act of 1937 ( 42 U.S.C. 1437f(o)(13)(B)(ii) ) is amended by inserting before or that the following: that house eligible youths receiving assistance pursuant to subsection (x)(2)(B), . (b) Income-Mixing requirement Subclause (I) of section 8(o)(13)(D)(ii) of the United States Housing Act of 1937 ( 42 U.S.C. 1437f(o)(13)(D)(ii)(I) ) is amended by inserting after elderly families the following: , to eligible youths receiving assistance pursuant to subsection (x)(2)(B), . 5. Applicability The amendments made by this Act shall not apply to housing choice voucher assistance made available pursuant to section 8(x) of the United States Housing Act of 1937 ( 42 U.S.C. 1437f(x) ) that is in use on behalf of an assisted family as of the date of the enactment of this Act.