Fourteen-year-olds Austin Stephanos and Perry Cohen are shown in this handout provided by the United States Coast Guard in Miami last week. Reuters

The search for Austin Stephanos and Perry Cohen stretched into its 12th day Tuesday off the coast of Florida as private pilots and sailors looked for any trace of the 14-year-olds who vanished on a fishing trip last month. But as concern for the boys' well-being has grown, so has the chorus of voices questioning whether they should have been out at all.

Austin and Perry grew up around the water, but critics have argued they were too young to be allowed to take their boat out unsupervised. As the case unfolds, it's become a national discussion: 14-year-olds can’t legally drive, smoke or vote. So should they be allowed to boat?

Experts said it's a tough question to answer, for a variety of reasons, not the least of which are varying state laws. They argue that how much freedom a kid should have on the water is a decision to be made case by case based on factors like local rules, weather conditions and the children themselves.

"You want your kids to develop independence skills, but part of our job as parents is to provide a perimeter of safety or a safely structured system," said Derrick Fries, who's won six world sailing titles and wrote the book "Start Sailing Right." "There isn't really any great way to train a kid for what I call 'open chaos' sorts of decisions -- that takes years of experience."

Florida Boating Fatality Rate | FindTheData

Many states, among them Arizona and California, require an adult to be on board when a minor is operating a personal watercraft or motor-powered vessel. But many do not. In Kansas, for example, adults are required only if the boater is under 12. In New Jersey, a child has to be 16. In Maine, a 16-year-old can supervise a 12-year-old, according to data compiled by the National Association of State Boating Law Administrators, a nonprofit based in Lexington, Kentucky.

Certification requirements get even more complex. About 40 states make boaters take a safety education program, but the age cutoffs for doing so differ. In Arkansas, California and Maryland, for example, there's no minimum age to take the boating safety test. But in New Hampshire, a candidate must be 16; in Colorado, 14.

In Florida, where Austin and Perry live, there's no age requirement for operating a boat -- they just have to take a safety course, which the boys did. People who use personal watercrafts, which are water scooters or jet skis, must be 14 or older.

Austin owned the 19-foot, single-engine boat they took out in July. It was his fourth boat. "These children are surrounded by water from the moment that they're born," Perry's mother, Pamela Cohen, told NBC. "Perry knew how to swim before he knew how to walk."

The duo was last seen on July 24 as they fueled up at a local marina. They were supposed to travel to a spot on the Loxahatchee River, which was as far as Perry’s parents would let them go, though they’d bragged on social media about cruising to the Bahamas. When a storm rolled in that afternoon and the boys didn’t pick up their cell phones, their families called the Coast Guard, which launched a desperate search for them but ultimately suspended it Friday with no results. Since then, the boys' parents have paid for their own search and rescue missions supported by a successful crowdfunding campaign.

Fries, the author, said he didn't let his kids operate his boats independently until they got their driver's licenses. He reasoned that the nation's waterways were less restrictive than its roads, so the variations in requirements didn't make sense. Too much can go wrong.

In 2014, 191 kids under age 13 were injured while boating, and 12 of them died. More than 400 teenagers were injured, and 34 died, according to data from the U.S. Department of Homeland Security.

Jessica Koenig, the executive director of the youth-focused sailing nonprofit Charleston Community Sailing in South Carolina, said how young is too young depends on the individual child. Her programs start training kids at age 5, but there are some exceptions for 4-year-olds. By age 8, kids can sail independently with an adult in a rescue boat "within yelling distance," she said.

Their education begins with safety. At Charleston Community Sailing, the kids spend days on land before ever touching water. Then they take a swim test, learn how to upright a boat and discuss the weather conditions before going out. "It's something a lot of parents want to teach their children," Koenig said. "Some kids really take to the water and some can be paralyzed by their own fears out there."

Mitch Brindley, the head coach of the sailing team at Old Dominion University and owner of Big Blue Sailing Academy in Norfolk, Virginia, said his philosophy is that there are two considerations when teaching young children about boating. "They have to be mature enough to understand the concepts and the actions," he said. And "they have to have the motor skills needed to do the required actions, whether it's turning the boat or balancing, stepping from one side to another."

Brindley said kids often learn faster than adults, but they don't always make the right decisions. The 12-year-olds he works with don't have the best judgment, but neither do the college students or locals in their 30s, he said. Brindley said he'd send his 10-year-old son, Pierce, out on his own locally but was unsure about a longer journey.

"Any number of adults, they've gone out and done the same exact thing that those kids do and they've never gotten in trouble. We never said, 'Hey, we shouldn't send adults out onto the water,'" he said. "The question is does a 13-year-old or 14-year-old understand the risk that's before him?"