Tim Klement is 70 years old but probably has to flash his driver’s license as proof. At a sinewy 6 feet 1, 170 pounds, he often passes for being in his 50s.

“He gets it all the time,” said Myra Klement, Tim’s wife of 25 years. “‘I can’t believe you’re 70. I can’t believe you can run this far. I can’t believe you’re in this great of shape.’ He doesn’t fit the mold of what people think of as a 70-year-old man.”

Come Saturday at the St. Jude Rock ‘n’ Roll Nashville Marathon, Klement will offer more proof that age is just a number by attempting to run his first road-race marathon. Anyone betting against the semi-retired St. Petersburg, Fla., entrepreneur finishing will be tossing money in the sky and watching it blow away.

The guy has already run the marathon in training too many times to count.

“I run them all the time,” Klement said. “Sometimes I run 30 miles. I’ve done marathons in training for four or five years.”

Boy Scouts are less prepared than Klement, who grew up in the Midwest, says he was the slowest runner on his high school cross country team and used running to manage stress during his professional career.

Klement is so detailed about preparation that in the past two months he tried four different mental approaches during training runs that stretched close to the marathon distance, the goal being to feel relatively fresh at the end.

In one workout, he broke the distance down into four 7-mile runs. “It tired me,” he said. “I couldn’t keep the pace up.”

In a second workout he broke down the race into three 8 3/4-mile runs. “It didn’t allow me to keep my pace,” he said. “You’re sucking at the end.”

Next, he sliced the race into two half marathons. “The first half was too long to make the second half work,” he said.

Finally, he hit a formula that worked, breaking down the workout into two 10-mile runs, topped by a 10K. “At 10 miles, it didn’t feel like I did anything,” he said. “The next 10 didn’t do anything. Then there’s only 6 miles and I’m like, ‘Wow, I can do this blindfolded.”

Klement does not think of himself an athlete.

“I consider myself myself someone who stays active,” he said.

He grew up in Council Bluffs, Iowa, then attended Cal, earning a degree in physiology.

Professionally, Klement worked in managerial positions at multiple companies, often hired to analyze, then oversee changes that increased the companies’ productivity and value.

“Sometimes I was a hired gun,” he said. “I really worked in a situation that a lot of people would have folded under the stress.”

Running represented his stress outlet.

“You go out on a run, enjoy that freedom, release stress and think,” he said.

He began running 5Ks in his 40s, then completed his first half marathon about eight years ago. He estimates he has run three dozen half marathons.

Wanting his first road-race marathon to be more than just crossing off a bucket list item, Klement signed up as a St. Jude hero and has raised nearly $1,000 for the organization, which focuses on children’s catastrophic illnesses.

Said Klement, “I had a mentor who taught me that when you understand you’re not the most important person in your life, you will succeed.”

Besides the fact that he’s 70 and older than probably 99 percent of the participants in Saturday’s marathon, Klement is different that most first-time marathoners in one other sense.

He’s not nervous.

“I know of a variety of ways that I can get from the start to the finish,” he said. “There are times I’ve been out in St. Pete and the temperature’s 80-85, the humidity the same. I was out running. I know how to deal with those types of issues, so I’m calm.”