A.J. Foyt, Johnny Rutherford, Al Unser and Mario Andretti all raced Indy cars for more than 30 years. They combined to win 185 races, including 12 Indianapolis 500s, and they secured a total of 15 championships.

And they all retired within the space of 12 months between May 1993 and May 1994, arguably leaving a void the sport has never recovered from in terms of star power.

The established stars of today's Verizon IndyCar Series are starting to challenge the legends of the sport in the record books. But they haven't captivated the masses in the same way that made Mario and A.J. household names since the 1960s.

Plus, in an almost changing-of-the-guard kind of way, three popular IndyCar Series veterans have turned or are turning 40. What does the future hold for elder statesmen Tony Kanaan, Helio Castroneves and Juan Pablo Montoya?

If they have anything to do with it, IndyCar has nothing to worry about. They're willing and able to ride their careers into their 50s, just like A.J., Mario, Big Al and Lone Star JR.

"I'll race until they don't want me," said Montoya, 39, who narrowly missed out on winning a second IndyCar championship this year, nearly half a lifetime removed from his first in 1999.

Montoya and Castroneves are both set for next year with Team Penske, and Kanaan expects to be back with Chip Ganassi Racing. But Kanaan has already experienced the challenges of being a veteran trying to hang on in the series as younger drivers try to take their place.

The 2004 IndyCar Series champion's career hung in the balance five years ago after he lost his ride with Andretti Autosport when sponsorship evaporated. Victory for KV Racing in the 2013 Indianapolis 500 put TK back on the right track and enabled him to land a ride with the top-tier Ganassi team starting in 2014.

Juan Pablo Montoya finished one point shy of winning the championship. He's showing no signs of slowing down as he approaches age 40. AP Photo/Eric Risberg

Even though he's the oldest man on the grid, Kanaan's strong drive to fourth place in the IndyCar season finale was a huge factor in his teammate Scott Dixon stealing the championship away from Team Penske's Montoya.

And while he finished eighth in the standings this year, the Brazilian believes he can still challenge for a championship.

"I still don't get it today when people say 40-years old is old," Kanaan said. "The champion [Dixon] is 35, Montoya and Helio and I are 40 and we're still going. I think it's just a number.

"I'm not planning to make that announcement anytime soon," he continued. "I'll last a little longer as long as I'm enjoying what I'm doing and as long as I'm competitive."

Sadly, part of the reason IndyCar lacks more seasoned veterans is attrition. 42-year old Dario Franchitti's career ended in an October 2013 accident at Houston, and late stars Justin Wilson and Dan Wheldon would be 37.

Greg Moore, considered by many to be the most promising IndyCar star of all prior to his death in 1999 at age 24, would have turned 40 this year.

That's not to say that IndyCar doesn't have a solid core group of talented drivers of all ages. The 30s are well represented, with series champions Sebastien Bourdais, Will Power and Ryan Hunter-Reay, plus race winners including Simon Pagenaud, Ed Carpenter and Charlie Kimball.

Twenty-somethings include Graham Rahal, coming off of a breakout year, along with fellow Americans Marco Andretti and Josef Newgarden. There's also 28-year old Canadian James Hinchcliffe and rising star Sage Karam.

Pagenaud, 31, ran the last year of the Champ Car sanctioned series in 2007, then bided his time in sports cars until he got an opportunity to return to the unified IndyCar Series in 2012. Last year, he joined Team Penske, where he appears poised to enjoy a long career with the sport's most successful team.

"Drivers come and go in phases; it's a generational thing and you can get lucky or not depending what age you're at," Pagenaud said. "You can't calculate when it will happen.

"I personally feel like I'm here at the perfect time, really. Hopefully we can build up for the next 10 to 12 years and then it will be my time to go!"

Today's drivers are different from drivers from the past in many regards. previous generations didn't take fitness so seriously, and the sport was frankly much more dangerous.

One constant is that there is always another generation of drivers ready to take over.

Team owner Bobby Rahal said he knew it was time to hang up his driving helmet when other opportunities outweighed his desire to race. Brian Cleary/Getty Images

"In the '90s, a lot of those guys left, but then you had me and Emerson [Fittipaldi] and Rick [Mears] and guys like that," said three-time IndyCar champion Bobby Rahal, who retired in 1998 when he was 45.

"When you're young and you're starting, the only thing you have in your life is racing," Rahal said. "Then you get married, you have kids, you get other business interests, and all those things start to chip away at your focus. To be honest, I didn't like assuming the risks on the ovals. If it had been a road racing series, I would maybe have stayed in there a few more years."

He added: "I would ask myself: Could I give 100 percent? And the answer, in all honesty, was no, because I had all these other things. For me, either you're there completely, or don't bother. So it was time to walk away."

The challenge for young drivers is to be in the right place at the right time to fill a prime vacancy on the rare occasion when a veteran in a choice ride walks away.

Pagenaud, with two drivers hitting 40 this year at Team Penske, looks to have put himself in good position. But then again, Castroneves doesn't sound like a man who is ready to hang up his helmet.

"I would say the 40s are the new 30s," Helio said. "Those guys [Foyt, etc.] didn't stop until they were around 50.

"For us, it's about the fun," he added. "We are all still competitive. Juan Pablo was leading the championship the whole way and age isn't stopping us. I was battling for the championship until the last race. I don't see myself stopping so soon. I still want to achieve my goals. It's all about the fire inside you. I still have plenty of fuel to burn and I guess time will tell."

Sage Karam has the potential for a long career with Target Chip Ganassi Racing. Mark J. Rebilas/USA TODAY Sports

At the other end of the career spectrum is Karam, who at just 20 has landed a plum part-time seat with Chip Ganassi's organization.

Karam hopes to follow the same kind of career arc that has made 24-year old Newgarden the sport's hottest property heading into this offseason.

"I feel like I'm probably in one of those prime spots," Karam said. "I'd say you need a good four years in these cars, just pounding away laps and miles and getting as much experience as possible. You're just seeing Josef becoming one of the stars of the sport and I think he's on his fourth year now."

Still, it would be tough to top the hunger of Montoya, who will turn 40 in September.

Stung by losing the 2015 IndyCar championship that he led from the start to Dixon -- and the very last gasp -- Montoya vows to return stronger than ever next year.

"We're testing in three weeks and I'm pumped about it," he said. "I don't switch off.

"Next year is not about making the Fast Six, it's about poles," he added. "This year we had probably five or six shots at wins and we took two. We probably want to win five or six races next year. That's the way I am and that's why I've been good at it all this time.

"I take no prisoners."