Rande Gerber on 25 Years with Wife Cindy Crawford: 'It’s Important to Remain Friends' (Exclusive)

It's been a year of anniversaries for Rande Gerber.

On May 29, the businessman, 61, marked 25 years of marriage with his wife, supermodel Cindy Crawford, 57.

Of the key to his and Crawford's longevity, Gerber tells PEOPLE in this week's issue: "It’s important in relationships to remain friends."

"Go out, have fun, laugh and try not to take life too seriously," he continues. "Let loose and enjoy the time that we do have."

Three days after his and Crawford's anniversary, Gerber and longtime friend and Casamigos Tequila partner George Clooney launched Cristalino tequila to celebrate their company's first decade in business.

"I can’t believe it's been 10 years, because it’s still as fun and as exciting as it was from the day we launched," Gerber says. "I knew back then that we created something that was different from other tequilas on the market, but we never thought, 'Let’s create the best-selling tequila in the world.' We’re extremely happy with where we are at today."

These days, the two friends are at different places in fatherhood: Gerber and Crawford's kids Presley, 23, and Kaia, 21, are all grown up, while Clooney, 62, is in the thick of parenting his twins Ella and Alexander, 5, with his wife, Amal.

"As [George's] kids get a little older and a little more active, I see George being the dad that I always knew he would be — totally hands-on," Gerber says. "Amal is also an incredible mom, which was obvious from the second I met her. There are definitely times when I see him and his kids running around and giggling with no pressure and no stress, and I’m like, 'Wow, I wish I could go back to those days.' But I love where my kids are now."

Presley is currently getting into real estate, and Kaia is already a successful model and getting more into acting. While Gerber says the kids do come to him and Crawford for advice "on occasion" about business and relationships, he tries "not to volunteer too much."

Despite his successful business career, Gerber says his proudest moment has "definitely" been "getting married and having kids."

"Nothing comes close, that’s for sure," he says.