* President Fernandez polls well among young Argentines
* Speculation swirls about Fernandez running again in 2015
* Midterms would be key clinching support for another run
* Strong Congressional support needed for third term amendment
Argentina lowered its voting age to 16 from 18 on Wednesday, a change that could help politically ailing President Cristina Fernandez court the youth vote ahead of 2013 mid-term elections.
Dozens of opposition members of the lower house of Congress walked out of the rancorous late-night session just before the measure won final approval by a vote of 131 to 2.
Fernandez, who polls well among younger voters, has not ruled out a bid by her supporters to change the constitution to allow her to run for a third term in 2015. Legions of youthful activists have joined the "Campora" movement, known for its rowdy demonstrations in favor of Fernandez's heterodox policies.
Skeptics say the new law is aimed at drumming up support for the president before legislative elections scheduled a year from now. Supporters say the measure aims to bring Argentina in line with progressive countries such as Ecuador and Brazil that have already extended voting right to people as young as 16.
Fernandez-allied lower house member Diana Conti said the bill "is neither opportunistic nor demagogic," but rather seeks "to widen the electoral base of our democracy."
The makeup of Congress after the midterms will be key to any effort by her allies to open the door to another candidacy. The 59-year-old Peronist leader won a blowout re-election last year and no strong opposition figure has emerged since.
But her popularity has fallen to below 25 percent as the economy gets hit by sluggish world growth, slowing demand from top trade partner Brazil, high inflation at home and government-imposed currency and trade controls that hurt confidence.
More than a million new voters are estimated to be eligible to cast ballots now that the bill has passed both houses. The Senate approved the measure earlier this month.
You still have to be 18 in Argentina to get married or buy alcohol or cigarettes.
Voting is compulsory for Argentines between the ages of 18 and 70 but it will be discretionary for 16- and 17-year olds under the new law.
Local Peronist party bosses may push to ensure high turnout from the new pool of teenage voters. But the benefits of the new law from Fernandez's point of view remain to be seen, said Ignacio Labaqui, who analyzes Argentina for emerging markets consultancy Medley Global Advisors.
"It is evident that an electoral strategy lies behind the promotion of the youth vote," he said.
"But despite being teenagers, young people live in the same country as other voters. So if the climate towards the government continues to deteriorate, the government's approval rating among younger people should also decline," Labaqui added.
Tens of thousands of demonstrators rallied in major cities last month to protest policies such as a de facto ban on buying U.S. dollars and a possible bid for a third term.
Fernandez has a working majority in both houses of Congress, but would need two-thirds' congressional support to convoke an elected constitutional assembly. The president has been coy about the prospect of changing the law to run again. Any such plan would hinge on the outcome of the midterm vote.
Because she has not anointed a political heir, analysts say Fernandez may want to keep speculation alive about a potential re-election bid in 2015 to maintain her grip on the notoriously fractious Peronist party and ward off "lame duck" syndrome.