P90X trainer Tony Horton is in the best shape of his life at 66. Here are his top longevity tips.

• Tony Horton, best known for the hit P90X workout, said he's thriving at 66 after tweaking his routine.
• Horton was diagnosed with a rare illness in 2017, and since then has followed a flexible plant-based diet.
• His current workout routine includes more yoga but also new challenges like obstacle courses.

Two decades after designing one of the best-selling home workout programs in history, personal trainer Tony Horton said he's in the best shape of his life.

When Horton's creation, P90X, hit the fitness industry in 2005, it became a smash hit. The program sold more than 3.5 million copies thanks to its high-intensity blend of circuit-style training, explosive movements, and plenty of core work.

By that point, Horton had a star-studded clientele, including celebs like Tom Petty, Billy Idol, Rob Lowe, and Usher.

Everything shifted in 2017, when he was diagnosed with Ramsay Hunt syndrome, a rare neurological disorder related to the shingles virus that can cause facial paralysis, ringing in the ears, and potential hearing loss.

Horton said the health scare prompted him to overhaul his routine, focusing less on hardcore workouts and more on recovery and stress reduction.

"I needed to add mindfulness components to my regular routine," he told Business Insider. "I looked more to resting, listening to music, taking a nap without feeling guilty about it, focusing on my family."

The upshot: doing less paid off, and Horton said he's now in better shape than ever when it comes to taking on adventures, including new physical challenges.

On a recent trip to Jackson Hole, Wyoming, Horton said he skied for six days in a row.

"I couldn't do that in my 20s and 30s," he said.

Horton's latest venture is Ninja Warrior and obstacle course training, navigating ropes, high bars, even the notorious "salmon ladder" at his tricked out home gym in southern California (which you can visit as part of the Paragon Experience event in May).

To stay strong and healthy into his 60s and beyond, Horton relies on habits like a flexible plant-based diet, lots of mobility exercise, and finding new challenges to keep things interesting.

"To maintain and sustain my athleticism, it's not just pounding the weights and running hills," he said. "Now it's really about quality of life and longevity and avoiding injury as much as possible."

He follows a flexible, mostly plant-based diet for longevity

Around the time of his diagnosis, Horton experimented with eating a vegan diet, and found he had more energy and better recovery after exercise.

While he's not strictly vegan now, he said whole, plant-based foods make up a majority of his diet.

Staples like beans, nuts, and seeds are a big part of his regular meals and snacks to make sure he's getting nutrients like protein and fiber for healthy aging.

"People don't realize there's a whole lot of proteins in plants," he said.

A typical day of eating for Horton includes seed bread with almond butter for breakfast, a protein smoothie with berries, banana, and cashew milk after a workout, and meals like lentil tacos for lunch and dinner.

Taking a more flexible diet approach and allowing for exceptions to the plant-based plan — like elk steaks on his ski trips, or desserts when his sweet tooth hits — keeps him from feeling deprived, so he can stay healthier overall in the long-term.

"Stick to your plan 80% to 90% of the time and every once in a while, eat that big beautiful chocolate chip cookie right out of the oven," Horton said.

Mobility training and balance training

As he's gotten older, while Horton doesn't work out any less, he's shifted his focus on training for longevity rather than trying to pack on as much muscle as possible.

He's still kept the muscle (Horton is no stranger to lifting heavy when it feels right) but his typical sessions include a lot more yoga and "animal flow," bodyweight exercise that emphasizes agility and graceful movement.

"Balance, range of motion, flexibility, and speed work are as essential as lifting weights and everything else," Horton said.

He also stays active by practicing with a slackline, a creative way of building balance and stability.

The key is consistency, finding time every day for exercise as a regular, habitual investment in your long-term health, just like staying on top of your finances.

"It doesn't have to be a lot. You can go for an 8-minute walk," Horton said. "But it has to be consistent. You don't pay your bills every fourth month."

New challenges keep him energized

Horton said one of his main strategies for staying youthful is finding creative ways to push himself, like Ninja Warrior-style obstacle courses.

It started when Horton was humbled by a rope climb, which he expected to be easier since he was strong enough to rep out dozens of push-ups and pull-ups. Rather than accept defeat, he decided to embrace the growth mindset, and obstacle training became a new way to stay motivated and get out of his comfort zone.

"The reason why I fell in love with it was because it was another level of challenge," Horton said. "Who cares if I fall or if I fail? Turn your ego off."