Editor's note: CNN alone will be in the support boats with Diana Nyad on her attempt to swim from Cuba to Florida. @MattCNN will be Tweeting live. Look for more updates on The Chart and follow her on the position tracker. And watch for Dr. Sanjay Gupta's documentary, "Diana Nyad:Xtreme Dream," Saturday, September 17, 8 p.m. ET
(CNN) -- Diana Nyad's personal test has begun. At 7:45 p.m. ET Sunday she jumped into the water and began her 103-mile swim between Cuba and Florida.
"I'm almost 62 years old and I'm standing here at the prime of my life," she said as she walked toward the sea. "I think this is the prime. When one reaches this age, you still have a body that's strong but now you have a better mind."
Nyad did a few stretches and played reveille, the traditional Army wake-up song, on a bugle before she dived in.
She likes a challenge. At 61, a lot of people are considering retirement and spending time with grandchildren. Not Nyad. For nearly two years, she's been training to set a record for open-water swims without a shark cage.
Nyad announced Sunday morning at a Havana news conference that she planned to enter the water at Havana's Marina Hemingway to begin her attempt.
"We're going to get started tonight," she said early Sunday as she stepped out of a car on her way to the news conference. "As you can probably tell, I'm pretty nervous. My adrenaline is flowing, but I've been training for two years.
"All my life, I dreamed of being the first one ever to swim across without a shark cage," she said, adding that when she turned 60, she "started thinking what if I went back and started to chase that elusive dream of Cuba."
One theory about Nyad's drive to make this swim is that she's avenging a failed attempt at this trip more than 30 years ago. And though Nyad admits there is some bit of athletic ego involved, she says it's more about proving to herself and to the world that 60 is not old.
"When I walk up on those shores of Florida, I want to prove to the AARP crowd that it's not too late to go back and write that book or adopt that child," she said.
On Sunday, she said: "The joke is the 60s are the new 40s, and it's true. ... I want to be there to say we have many, many years of vitality and strength and service left in us."
The swim was planned for summer 2010, but was called off because of bad weather. She continued to train.
Immense planning and logistics go into making an attempt like this.
First, the sheer amount of training it takes to get her body in shape is remarkable: Almost two years of daily six-, eight, 10- or 12-hour swims.
She's faced political as well as physical challenges. Nyad is determined to swim from Cuba to Florida. Getting permission from both sides took several months. At several points along the way, bureaucratic snags threatened to tank the whole operation.
Nyad's team of more than 30 people consists of about 10 handlers, who will take turns minding Nyad's every move for the estimated 60 hours it will take her to complete this swim. Boat captains will take shifts driving the five boats in Nyad's small armada.
Six ocean kayakers will switch off paddling kayaks mere inches from Nyad's side throughout the journey, towing underneath them electronic Shark Shields that emit a harmless but annoying electrical impulse that repels most species of sharks. Shark safety officers trained to distract any creatures that may get curious will take turns in the water surrounding her.
"There's no getting around the fact that we're in an ocean here where some dangerous species of shark swim," she said at the news conference.
She said the whitetip shark, however, wasn't bothered by the Shark Shields, so she will also have shark divers on hand to help distract them. "Nobody is going to use any lethal weapon on this swim," she added.
A team doctor will also be on board to monitor Nyad's hydration and nutrition and to tend to any bites or stings from jellyfish, Portuguese man-of-war and other sea creatures. The navigator will ensure Nyad is swimming in the right direction and guiding her to avoid detrimental ocean currents.
CNN will have a crew of seven on board, as well as a special marine tracking satellite dish to provide live pictures of the swim.
A sixth boat carrying Nyad's friends is expected to join the flotilla for the last several hours of the trip, and an equally large team of people will be standing by on land to witness the end of the swim.
Nyad will be burning tens of thousands of calories. She will be replacing that energy with nutritionally rich fuel. Every hour, Nyad will stop swimming for just a few minutes to take in food and hydration. A typical meal at one of these pit stops may include hard-boiled eggs, protein gels or peanut butter and a few ounces of an electrolyte-filled beverage.
Dr. Ken Kamler, a microsurgeon and expert on practicing medicine under extreme conditions, says that as Nyad swims, her body will first turn to glucose for energy. Once her body burns through that available sugar, it will next start burning body fat as fuel, and finally turn to protein once her fat stores are exhausted. Once her body starts burning protein for energy, he says, she will be in a race to hit Key West before her body destroys muscle tissue.
Nyad is undaunted. "I am a better athlete today than I was at 29," she told CNN.
CNN's Shasta Darlington in Havana, Cuba, contributed to this report.