Bill Rancic gears up to run New York City Marathon

Bill Rancic has run marathons before, but never like this.

For one, he's 42 now -- older than when he ran a 26-mile course first at age 28, and again at 30. He wasn't married back then, didn't have kids, work wasn't as busy. And he probably didn't start those marathons in last place.

Come Sunday, that's exactly what the TV personality and businessman will be doing at the New York City Marathon. He'll begin the race dead last, and for each person he passes, Timex is donating $1 to Fab-U-Wish, a breast cancer charity started by his wife, Giuliana Rancic (who's survived the disease herself).

"It was an opportunity to raise money for a good charity, something that's near and dear to our heart," Rancic told CBSNews.com of why he signed up for the race.

It also provided a personal challenge -- could he do it again, now that he's in his 40s? "I think every guy that hits his 40s has a little bit of a wake-up call and wants to just keep things real, as they say, and just to push yourself," he said. "For me, it was important to just prove to myself that I could do it."

Rancic says he hopes to pass 25,000 people (thus raising $25,000) as he runs the race. How long it takes him to finish, however, is up for debate.

"A month ago I said I wanted to come in at 4 [hours], but now, I don't know. It's gonna be touch and go," he said. "I've had just a crazy week of traveling and business stuff and, it depends on if I can get some good rest the next couple of days."

Rancic has been training for months, running anywhere between 20 to 40 miles a week. The longest run he's done while preparing was 18 miles. Initially he put together a music playlist to run with, but has instead been training with his cousin Tommy and friend Ari, where they've talked "about life, and the world, you name it -- the topic of discussion varies from mile to mile."

Running is a family affair for the Rancics. He and Giuliana go running together, he said, and when they were dating they "planned our whole life on those runs." Their 14-month-old son, Duke, also gets in on the action with the help of a jogging stroller.

"He went on a couple of my training runs with me, and he's a trooper. He loves it, he loves getting out there, loves the wind in his face. He's a people watcher." Rancic said. "It's great bonding time."

Little Duke, who was a bear for Halloween, is "babbling a lot," according to his dad, who says he's "all boy." "He's just a bruiser, loves roughhousing, getting thrown around and swings and slides, and I think he's gonna be into sports. I can tell already."

Starting the race in last place will be intimidating for the self-described "competitive guy," but Rancic says it will be worth it.

"It's going to be daunting knowing that there are 40,000 people in front of me, but the good news is for everyone I pass, Timex is going to donate $1 to my wife's breast cancer charity," he said. "So as intimidating as it is, it's also very rewarding because literally everyone I go by, I know it's going to a good cause."

Rancic won't be resting much after crossing the marathon's finish line. He and his wife are doing a seventh season of their "Giuliana & Bill" reality show for E!, and he's working on another reality series called "Training Day" with Ridley Scott where he will be embedded "with some of the most dangerous professions out there." The couple is also expanding their restaurant business -- they've got RPM Italian in Chicago, will be opening RPM Steak there in the new year and just broke ground on another RPM Italian in Washington, D.C.

Do all those plans include one to add to their family? "We'll see!" Rancic said. "I think if we're gonna do it we want to do it sooner rather than later, and keep the kids close in age."

As Sunday approaches, Rancic says this year's New York City Marathon will be particularly meaningful, after last year's event was canceled following Superstorm Sandy and in the wake of the bombings at the Boston Marathon in April.

"I'm here in New York today and the excitement is brewing, it's unbelievable," he said. "And I think certainly with Sandy last year and then the incident that happened in Boston I think this is going to be a real victory for everybody."