The boys of Greta Van Fleet sure do put on one heck of a rock show. This group of youthful Michigan longhairs — three brothers, one friend — had a sea of fans young and old banging their heads at the Miller Lite stage of ACL Fest on Friday for their 4:45 set, which brought to mind the glory days of early '70s, when rock was king and flower power was still strong.

Hailed by many — even a wry Robert Plant — as the second-coming of Led Zeppelin, Greta Van Fleet delivered on that promise and then some, riding sick riffs and pounding out heavy jams as vocalist Josh Kiszka grinned and wailed and grooved across the stage with his fringe and feather accessories swooshing accordingly. Star power is an understatement.

Though band members have been playing together for about six years, they’re all still only in their late teens and early 20s, a fact that suggests much to be excited about and explains some things as well. The four-piece’s musicianship is absolutely stunning; guitarist Jake Kiszka played one searing solo with his guitar behind his back for a remarkably long time. And it sounded, like, really good. Drummer Danny Wagner, shirtless with a bolo tie and necklace, closed out the set with a ferocious solo. And Josh Kiszka’s howling frontman presence displayed a vocal control and comfort far beyond his years.

Going '70s for Greta Van Fleet means really going there, with trope-filled songs about “finding your freedom,” as well as a barefooted bassist and a good number of cries of “oh mama" and declarations that “I’m gonna get your lovin’ baby.” Fortunately, it all sounds really good coming out of Josh Kiszka’s mouth. I’m extremely eager to see the band’s lyrics develop and grow more precise with time.

Rather than drawing inspiration from a previous era, the band is essentially just replicating it. But as much as I wanted that to drive me nuts, they just did it too well — with too much energy and spirit and joy — to not completely win me over.

And the people love them. The band’s new album "Anthem of the Peaceful Army" comes out in just a few weeks, and a few starry-eyed front row die-hards already had a bandanna with the words “Peaceful Army” to hold out in support. At certain points during the set, the crowd made peace signs with their fingers, and when Wagner and the three Kiszkas bounded off the stage after their final song, chants of “one more song” lingered until the tech crew was well into their set change.