When Bill Purdin was 54, he decided his scuba diving hobby was too tame. So he took up skydiving instead.

"I liked to do ocean scuba in the winter," recalls Purdin. "It was February and I was just going to watch the sun come up. I'm down there in the dark and there was a soothing surge back and forth and I fell asleep."

Though he wasn't in any danger - water seeping around his mouthpiece woke him up before too long - Purdin says the incident made him think about finding a more stimulating pastime.

"I realized I need something a little more exciting," he says. "(Scuba diving) was getting a little boring."

Four years later, Purdin is a licensed instructor with more than 1,200 skydives under his belt. He was the nation's oldest skydiving instructor to complete the rigorous Accelerated Freefall training, he says.

Now 58, Purdin says learning his new hobby was as simple as searching online for a "drop zone," a skydiving facility where experts take novices on their first jumps.

For first-time skydivers, the most important thing is to find people who will take the time to make sure you're comfortable jumping out of a plane 15,000 feet in the air, he says. He advises looking for an instructor certified by the U.S. Parachute Association.

"Find a drop zone that has instructors who are doing it for the love of the sport, and secondly who are willing to give the time necessary for a safe and enjoyable experience," says Purdin, who is an instructor at Skydive Pepperell in Pepperell, Mass.

"Make sure your head's on straight and you haven't accepted the misleadings that because you're at 50 years old or older, you're somehow an inferior human being. ... It's all about finding the person and the drop zone that has the program you really want."

The only physical requirements are that you weigh less than 225 pounds and are in reasonably good shape, he says.

"Your frame and weight should be in really tight proportion. As far as reflexes or medical stuff, I don't think there are any impediments," says Purdin.

Novice skydivers will spend a couple of hours in on-the-ground training, he says, during which instructors will make sure you know exactly what you're getting into and just what the risks are.

"You're going 120 miles per hour three miles up in the sky," Purdin says. "You need to think about that ahead of time."

The instructors will make sure you don't have any medical conditions that would disqualify you from jumping. They'll explain the equipment and train you on gearing up, boarding the plane, jumping out of it and how to handle freefall.

First-time skydivers go in tandem, meaning they dive attached to an experienced instructor who handles deploying the 'chute, guides the descent and makes sure you both land safely on the ground, says Mike Johnston, who runs a drop zone called Skydive DeLand in DeLand, Fla.

"One of the benefits of it is that you're together with an instructor who operates all the equipment," says the 58-year-old Johnston, who has nearly 7,000 skydives to his name.

"It just becomes an enjoyable experience that doesn't require that you're on your own. It's a very popular thing for people on their birthdays. A lot of people in their 60s, 70s and 80s come out."

Even the mother of Skydive DeLand's owner regularly goes out on jumps, Johnston says.

"She's 86 now," he says. "She' got something like 60 tandem jumps. Most all of those occurred after she turned 78."

In Pepperell, Purdin says his drop zone also gets its fair share of older skydivers.

"We've had people come out who are 80 years old and on walkers," he says. "We recently had a guy who was 88 years old. His last jump was in World War II when he bailed out of his B17. He said, 'This time I want to choose to jump out of the plane,' and he did and he had a blast."

As for the potential risks, Purdin says his equipment has malfunctioned three times. All three times his training and backup equipment worked perfectly, he says.

"It only encouraged me in the sport," Purdin says.

"There are two kinds of people I know now that take up skydiving. One of them says, 'What time is lunch?' The other says, 'What time can I get back on that airplane?'" he says. "There's something about being in freefall that some people just love. There's nothing like it."

There are drop zones in almost every region of the world. Check www.dropzone.com for a complete list.