Up until Friday, the emergency contraception, also known as Plan B, was only available to women 17 and older. The morning-after pill contains a high dose of a female hormone and can prevent pregnancy if taken soon enough after unprotected sex by preventing a fertilized egg from embedding in the uterus.
The ruling by U.S. District Judge Edward Korman overturns a decision by Health and Human Services Secretary Kathleen Sebelius. The Justice Department didn't immediately say whether it would appeal the ruling.
The ruling is the latest twist in a decade-long push for easier access to emergency contraception. The FDA was actually preparing to lift all age limits on Plan B One-Step in 2011 when Sebelius, in an unprecedented move, overruled her own scientists.
Sebelius said some girls as young as 11 are physically capable of bearing children but shouldn't be able to buy the pregnancy-preventing pill on their own. President Barack Obama said he supported the decision, also citing concern for young girls.
That move shocked women's groups. In his ruling, Korman blasted Sebelius for what he called a political decision. The judge noted that many over-the-counter drugs are dangerous for children, but are still sold nevertheless without age requirements, while "these emergency contraceptives would be among the safest drugs sold over-the-counter."
The ruling doesn't sit well with many parents.
"Why tell your parents when you can just go do these things, and then if something happens, let me go run to the store," said Monique Kauroma of Los Angeles.
The Center for Reproductive Rights and other groups have argued that contraceptives are being held to a different and non-scientific standard than other drugs, and that politics has played a role in decision-making.
Advocates say many people oppose the ruling because they don't understand what emergency contraception is. A 2003 Kaiser family foundation study found 75 percent of adults don't know what it is or they thought emergency contraception was the same as the abortion pill.
Social conservatives criticized the ruling, saying it puts the health of young girls at risk.
"There is a real danger that Plan B may be given to young girls, under coercion or without their consent. The involvement of parents and medical professionals act as a safeguard for these young girls. However, today's ruling removes these commonsense protections," said Anna Higgins of the Family Research Council.
Taking the morning-after pill within 72 hours of rape, condom failure or just forgetting regular contraception can cut the chances of pregnancy by up to 89 percent. But it works best within the first 24 hours. If a woman already is pregnant, the pill has no effect.
If the court order stands, in 30 days, Plan B One-Step and generic versions would become as easy to buy as aspirin.
The Associated Press contributed to this report.