From PEOPLE Magazine Click to enlarge
The minute he discovers his buddy Kenny Chesney has never heard Bruno Mars's music, Tim McGraw halts a photo shoot to grab his iPod. Scrolling through, he settles on "Count on Me," turns it up, snaps his fingers and sings along. "I hear this stuff 'cause I got three daughters at home," he explains. "I can turn you on to One Direction if you want!" Chesney pauses, then says with a laugh, "I don't even know what that is. I'm so out of the loop!"

This summer he'll have plenty of time to learn from McGraw. The longtime pals have just kicked off a monster 23-date tour, their first together in 10 years. "We can remember sitting in each other's apartments 20-some-odd years ago, playing guitar and dreaming about getting the chance to do anything with our music," says McGraw. "And here we are playing stadiums. It's mind-boggling."

It's been a long road since they first met as struggling singers in Nashville in 1991, but, they insist, they've only improved with time-and not just musically. "We're definitely both in better shape," says McGraw, 45, who credits his decision to quit drinking four years ago for his own fit physique. Adds Chesney (whose 13th album, Welcome to the Fishbowl, is out June 19): "I know I'm 44, but part of me still feels 18, and I love that. I just can't act 18 anymore."

In fact, instead of planning how they'll party together, the guys are thinking about fitting in workouts and hitting the softball field. "Who knows, Tim and I might crash a church league somewhere!" says Chesney, who may have a harder time persuading McGraw to try his favorite tour-bus pastime: PlayStation football. "Kenny's a bachelor-he has no clue!" cracks his tourmate. "I haven't played video games since college."

Audiences are sure to witness their brotherly bond during their shows, which feature a joint set (they even sing each other's songs) and solo performances. Still, the pair's affection for each other only runs so deep. Jokes Chesney: "I tell you what we won't be doing on tour: love-ballad duets!"