A charter amendment to lower the voting age to 16 that will appear on the November ballot would put San Francisco at the forefront of expanding voting rights at a time when some other governments around the country have implemented increasingly restrictive voting laws.

“Regardless of whether this measure is approved or not, (San Francisco) is starting a trend that will happen across the country, where cities like ours will consider whether young people can vote,” Supervisor John Avalos, who championed the measure, said at Tuesday’s Board of Supervisors meeting. The measure would allow people as young as 16 to vote in city elections.

The board voted 9-2 to place the measure on the ballot, reflecting a change of heart by several supervisors who initially indicated they were opposed to the measure.

Some of them changed their minds after a hearing last week during which dozens of young people testified in support of the proposal, which is also unanimously supported by the San Francisco Board of Education. And they were swayed by the idea that lowering the voting age gets people involved in the electoral process earlier, which in turn could make them habitual voters — a step critical to improving the country’s low turnout rates.

Bucking national trend

But some supervisors also pointed to the rise of Donald Trump, the presumptive Republican presidential nominee, as evidence that adults are no more informed than a 16-year-old.

“I don’t think 18-year-olds and older have a lot to brag about, and I actually think if you gave 16- and 17-year-olds a chance ... they would do a lot better than we are,” Supervisor David Campos said.

Lowering the voting age runs counter to laws in many states to implement strict voter ID requirements and limit the time frame during which people can vote.

A Kansas law that took effect in 2013 requires residents to provide proof of citizenship when they register to vote. It is one of four states with such a law. A 2013 North Carolina law eliminated residents’ ability to register to vote and cast a ballot on the same day and also cut early voting by seven days.

In 2016, 17 states will have new voting restrictions in place for the presidential election, according to the nonpartisan Brennan Center for Justice in New York. The laws range from new ID requirements to registration restrictions and a shorter time frame for early voting, according to the center.

Such measures are in stark relief to the charter amendment to go before San Francisco voters in November. If it passes, San Francisco could become the first major U.S. city to lower the voting age.

Council members in Washington, D.C., are considering legislation to allow 16- and 17-year-olds to vote in federal elections, a measure even more radical than San Francisco’s. Two other municipalities have lowered the voting age in local elections to 16 — Takoma Park and Hyattsville, both in Maryland.

“When this first came up, my initial, knee-jerk reaction was ... not so favorable,” Supervisor Scott Wiener said Tuesday. He changed his mind after reading more about it. “There are so many 16- and 17-year-olds who will be passionate, intelligent and thoughtful voters.”

Some opposition

While it was clear from the outset at Tuesday’s meeting that the measure had the eight votes it needed to go on the November ballot, two supervisors, Mark Farrell and Malia Cohen, voted against it.

Farrell said current laws create a patchwork system for young people: They can drive at 16, vote at 18, and purchase tobacco at 21. Gov. Jerry Brown signed legislation earlier this month raising the age to purchase tobacco.

“The age limits we have imposed are incredibly inconsistent and, truthfully, just don’t make sense from a macro perspective,” he said.

Cohen echoed that sentiment. “We want to lower the age to vote to 16 but we are raising the age to purchase tobacco to 21,” she said.

She also said she was worried that lowering the voting age would give rise to more 16- and 17-year-olds being treated as adults in the criminal justice system.

“It’s a very slippery slope when we make the argument that if one can vote, one should be able to stand trial,” Cohen said.

Supervisor Jane Kim countered that the fact that 16- and 17-year-olds can be tried as adults is “all the more reason they should be able to vote and have a say in our criminal-justice policies.”

Practically speaking, the measure would impact a small percentage of possible voters — around 11,000 youth out of 450,000 registered voters in San Francisco.

On notifying the feds

Also on Tuesday, the Board of Supervisors briefly addressed one of the most contentious measures it faces — legislation barring city law enforcement officials from notifying U.S. Immigration and Customs Enforcement agents when an individual in the country without legal standing will be released from local custody, except in very limited circumstances.

Newly elected Sheriff Vicki Hennessy wants greater discretion to notify federal immigration authorities — a position backed by Mayor Ed Lee. Avalos, who introduced the legislation, said Hennessy’s proposed policy “does not fit into the values of San Francisco.”

But he said he wanted to work with Hennessy to come to an agreement. “I would like to hold out some time to try and get there,” he said.

The Board of Supervisors will take up the legislation again May 24.

Emily Green is a San Francisco Chronicle staff writer. Email: egreen@sfchronicle.com Twitter: @emilytgreen