"The minimum age for a prostitute is raised from 18 to 21 years," the Dutch capital city announced in a statement, and said the new rules are meant to fight industry abuses and "strengthen prostitutes' position."
The city also wants brothels in Amsterdam's landmark red-light district to close between 4.00 am and 9.00 am (0300 GMT and 0800 GMT) on weekdays and from 5.00 am (0400 GMT) on weekends.
"At the moment, there isn't much surveillance and social controls during these hours," it said, noting that as a result "it is more dangerous to work and prostitutes have to deal with drunk and aggressive clients during these hours."
With an estimated 5,000 to 8,000 prostitutes, the city's red-light district attracts sex tourists from around the world to a country long considered one of the world's most liberal.
Observers have pointed to a move in recent years towards conservatism, including efforts to curtail legal soft drug use and prostitution.
Amsterdam says it wants to decrease the number of sex workers in a move to fight crime generated by prostitution, which was legalised in the Netherlands in 2000.