Jacinto Bonilla, 80, is not your average grandpa. He has a six-pack, and his muscles are cut like a professional athlete. His secret? He's been doing CrossFit for 12 years. 

RELATED: The One Ab Exercise You Can Do Anytime — Anywhere

"This guy is amazing," celeb trainer Bob Harper says, who has also been a huge fan of CrossFit for a long time. 

"I've loved CrossFit for years," he tells us. "I like that the movements are so functional, it's not just about doing things your body wasn't meant to do. It's about being able to sit down in a chair and being able to stand up, just being mobile."

And Rach can vouch for Bob.

"He loved CrossFit before CrossFit was cool," she says.

Naturally, Bob jumped at an opportunity to train with Jacinto at a CrossFit gym in New York City. 

As for how he got into CrossFit, Jacinto says that he was looking for a way to spice up his workout routine. 

"I was doing circuit training, and I wanted to change my routine," he tells us.  

Not to mention his scary prostate cancer diagnosis in 2008. He beat it, but it led to a painful blood clot in his chest. It made him realize how fragile his health was, so today, he does what he can in the gym to stay healthy.

"I don't want to end up having any attacks of any kind," he says. "That's why I keep going. Even though there are times when I don't work out as hard, or I'll be screaming through my workout. But it's great being able to do things a lot of people are not able to do or are not willing to do."

Bob can relate. He suffered a near-fatal heart attack in February 2017, which is one of the reasons he continues to hit the gym.

At the gym, Jacinto led Bob in a full CrossFit workout. He had Bob do as many of the following exercise rounds as he could in three minutes, followed by one minute of rest. Then they did an additional five rounds.

• 3 power cleans
• 6 pushups
• 9 squats

Of course, Bob was breaking a sweat. (We know we would be!)

"That was a good workout. I was just trying to keep up with Jacinto the whole time!" he told us after his workout ended.

If you're looking to give CrossFit a try, Bob and Jacinto have three tips to help you get started:

1. Start with weight training.

"I'm a big believer in weight training," Bob says. "Weight training is the fountain of youth, and if you're pushing some sort of weight at least one time a week, don't be afraid that you're going to build up and have these (bulky) muscular bodies."

2. Start off small.

"You're not going to go in and be a superhero that day. You just have to go in and commit to having A workout, not THE best workout ever."

3. Set manageable goals.

"We were saying when Jacinto goes to the gym, he's working out with all these very young people," Bob says. "And he's just doing the best that he can do, and that's what CrossFit's about. It's not about being able to go to the CrossFit Games and be a huge hero. It's about just doing what you can do."