Analysts say such announcements could be part of the government's efforts to gain support among young voters. Iran's Parliament in 2004 raised the legally acceptable age of marriage for girls to 15 from nine.
"The best age for marriage is between 16 to 18 for girls and 19 to 21 for boys," the Mardomsalari newspaper quoted Ahmadinejad as saying.
Ahmadinejad's popularity has been harmed since the disputed 2009 presidential vote, which the opposition says was rigged to secure his re-election. The authorities deny this. The vote and its aftermath created a rift within the ruling hard-line elite.
"We have a parliamentary election in 2012 and hard-liners want to win young people's votes in order to win the assembly vote," said an Iranian political analyst who asked not to be named.
Iranians struggle to cope with international sanctions and deepening economic uncertainty. The official inflation rate is about 10 percent and unemployment about 15 percent.
Iran has been hit by foreign sanctions over its disputed nuclear work, which the West fears is a cover to build bombs. Iran says its nuclear program is peaceful.
The authorities have been encouraging marriage as a way to fight what they call the "spread of immorality among youth."
Some hard-line clerics and lawmakers have warned over increasing rates of divorce.
"Divorces ... are increasing. High prices have caused problems for ordinary Iranians," said prominent cleric Grand Ayatollah Nasser Makarem-Shirazi on Friday.
Female activists criticize laws relating to women, including those that restrict women's divorce and custody rights and forbid them from working or leaving the country without their husband's permission.
A woman's testimony and life, in blood money terms, are worth half that of a man's in court. A woman cannot become president.
Activists say women's demands cannot be put on the back burner in a country where two-thirds of the population is under 30 and more than 60 percent of university graduates are women.
Iranian women have made inroads into politics and business in recent years. Shirin Ebadi, a human rights activist, was awarded the Nobel Peace Prize in 2003 for her work on women's and children's rights in the Islamic Republic.
