It's not clear what about the age-residency requirement you find objectionable. Congress is determining under what conditions a child born abroad is granted citizenship at birth. Requiring the U.S. parent (of of "mixed" nationality couple) to have spent a stated amount of time in the U.S. after that person has attained what might be called an "age of reason" (high school age) seems related to the goal of assuring the child has a parent who has a grasp of the meaning of U.S. citizenship.
This particular element of the law has not, to my knowledge, been challenged. But in related contexts, the U.S. Supreme Court has upheld challenges to post-citizenship residency requirements (Rogers v. Bellei (1971)) and to rules for out-of-wedlock births which make citizenship for the child more stringent when the U.S. parent is a male than when the parent is female. (Nguyen v. INS (2001)).
I was reacting to the statement in Comment #74 that Obama’s mother wouldn’t have been eligible in 1961 because she was 18 year, 9 months, rather than 19. Most people graduate from high school at the age of 18, not 19. Also, if I remember correctly, 18 year olds (mostly males) were eligible to die in combat at age 18.