(CNN) -

Every morning before riding, Gary Stevens has to walk four miles.

The walk is a necessity, the only way the 51-year-old can get his ailing knees slowly warmed up and working, capable of dealing with the demands on those damaged joints of riding some of the world's best horses at speeds of up to 45 mph.

When the American first retired in 2005, he had enough money in the bank from a glittering riding career to kill any thought of a comeback. Then there was the ensuing broadcasting career, not to mention acting forays in the movie "Seabiscuit" and the television series "Luck."

But he finds himself back in the saddle. "This is middle-aged crazy," he says -- and without cracking a smile, all too aware of the risks being taken.

One only has to watch the clip of him being trampled like a rag doll in the 2003 Arlington Million race, suffering a punctured lung and a fractured vertebra in his back, to see that.

"People retire and play golf or go fishing. This is my fishing. I never thought I'd say so at this time of my life but I'd rather be on the race track than on the golf course, and I like golf," says Stevens, who started racing again at the start of last year.

"And the 50s are the new 30s right? Anyway, I'm not the only old guy out there. Look, you've got Fred Couples in golf and he's doing alright."

But his return demanded sacrifices. Stevens had to shed the equivalent of 10 bags of sugar off his body and get down to a racing weight of 114 lbs (51.7 kg) in a grueling two-month training regime.

In addition, his knees are damaged to the point he knows he will need surgery to replace them.

"You don't realize how good it is until it's gone," he told CNN, explaining his decision to retire.

"Being retired allowed me to look back and actually enjoy some of the great things that had been accomplished in my first career. I was like 'wow.' If you won a big race, you could never rest on your laurels as there was the next day, the next race.

"Then there were the injuries and always thinking and obsessing, 'When will I get back?' I realized how good it was and I asked myself, 'Can I do it again?'

"I didn't want to come back and tarnish what I'd done in the past. I wanted to come back at a high level."

Sporting comebacks don't generally tend to end well. Stevens, though, has provided a Hollywood epilogue befitting his secondary career on the silver screen.

Last year, he won 69 races including the prestigious Preakness Stakes and the Breeders' Cup Classic, and he is fast approaching 5,000 career victories on American soil alone. He notched up $100 million in winnings by the age of 30, and he is now nearer the $225 million mark.

There are parallels between Stevens and another giant of flat racing, Lester Piggott, who famously returned to the saddle aged 55 -- in his case after a year in prison for tax evasion. Much like Stevens, his success was almost immediate, the British rider capping his return by winning the Breeders' Cup Mile within 10 days of his return.

"It's funny," says Stevens, "but no-one's actually asked me about the Lester link before. The way he rode that Breeders' Cup, arguably one of the best rides of his career, making all the right moves at the right time. So my thought was, 'If he can do it and I'm younger, then why not.' The guy was a bit of an inspiration."

Luck has also played a part in Stevens' return to the saddle. He had previously been enjoying an acting career in the Michael Mann-directed TV series "Luck" alongside the likes of Dustin Hoffman and Nick Nolte, but it was cut short before the second season began due to concerns over animal safety.

"If that hadn't been axed, I'm not sure I'd be doing this," he says. "I was all set to meet in makeup the next day at 4.30 a.m. when I got an email saying it might be scrapped.

"Via a couple of phone calls a few minutes later, sure enough, it was over. I was just lost, it was like losing a family member. In that first week, I made the decision to come back."

Stevens will forever be grateful for his acting career -- he describes it as one of "two dream jobs I've had" -- but it has also acted as Cupid for him, having met his wife Angie on the first day of filming "Seabiscuit."

"I turned up on the set and this lady appeared as a silhouette. She said, 'You look lost,' and I was like, 'I need to find where I'm supposed to be.' I explained I was playing George Woolf and she showed me to my trailer."

He did not lay eyes on her for the next five months but, as the movie wrapped up, they met again, went for dinner and the rest is history.

Such Hollywood-esque nuggets are littered throughout the life of the man from Caldwell, Idaho.

There was the hip condition called Perthes syndrome that forced him to wear a metal brace for 19 months at the age of seven, his decision to drop out of high school in 1979 to become a jockey -- also the year he won his first race -- difficulties with alcohol in his career, and now the ongoing return to the sport of kings: all quite remarkable for a grandfather.