The great joke of Willow Smith's "21st Century Girl" is that she actually is one. Born in the year 2000, she's not the only star in post-millennial tweens' consciousness, but she's indisputably the most important one who's one of them. If "Whip My Hair," which I wrote about here a few months ago, was the song in which Willow announced that she had arrived, this one's the one in which she starts insisting on her own significance and power—trying to call that power into being by naming it, in fact.

Like a lot of tweens' self-presentation, Smith's is brash, happy, and almost totally built on identifiable bits of her parents' generation. The "eh eh" bits of "21st Century Girl" are totally Rihanna; the idea of a "beautiful life" in a song like this, and the way she sings the phrase, belong to Ace of Base's song of the same name. And I can't hear Smith purring "I'm the type of chick that likes to rock the beat" without thinking of Robyn's delivery of practically every line in "Konichiwa Bitches," back when Willow was four.

Fair enough: modernity is post-modernity, and if Smith's "new girl thinking" isn't all that new, at least she's facing it with a smile. Of course, young Willow wasn't the first person to declare her modernity in almost the same terms. Kids always think they invented youth.

The most impressive variation on the child-of-the-century gambit came from the British rock band T. Rex, who had a massive, enduring hit with "20th Century Boy" in 1973. (The joke for them was a little less sweet: frontman Marc Bolan was playing for the tweens, but he was 25, practically ancient in the pop terms of the time, and had already been making records for six years. And Bolan wouldn't live to see the next century, dying in a 1977 car crash.) Despite what Willow Smith's T-shirt suggests, Bolan didn't need any training: all the bravado of his presentation came through in his delivery, and even though his lyrics mean as little as hers, the only real clichés in them are song commonplaces ("I wanna be your man," "it's plain to see you were meant for me"), not self-esteem commonplaces.

In fact, the words of "20th Century Boy" matter so little that Bolan slurs the first line of the song into incomprehensibility. "Everybody says it just like"—what's the word? "Rock 'n' roll"? "Robin Hood," as the rhyme suggests it should be (and later covers enunciate)? Something else? How does everybody say it? He's a toy, he's a boy; he's a playmate for tweens, he's a plaything for the kids. And he's fully realized: if Willow's hoping to pull gold from her soul at some point, Bolan's already offering solid gold easy action.

If you're being sold as the soundtrack for youth, though, you might as well sell yourself as the sound of the future. The joke of Sigue Sigue Sputnik's 1986 single "21st Century Boy" was that it was a con that everybody in their audience was in on. The band were a tongue-in-cheek, dystopian vision of what a pop act could be—maybe the only rock group in history to present themselves as much more cynically packaged than they actually were. (They even sold advertising space between the songs on their first album, Flaunt It.) Their frontman, Tony James, was already in his 30s by the time the band got underway, but he was obsessed with new boy thinking. He'd spent a few years playing in Generation X, Billy Idol's first band, whose early songs included "Youth Youth Youth" and "Wild Youth."

"21st Century Boy" is barely a song at all: a single nagging, ultra-stupid riff, a bunch of sound effects, and a string of keywords, catchphrases and brand names. If its lyrics landed in your Twitter feed, they'd have hashtags all over them and you'd think somebody had gotten their account hacked. It needs training a lot more than Willow Smith's song, or Marc Bolan's. But for all its incoherent bluster, it might be a more accurate vision of the new century than either of its titlemates: ADD-addled, videogenic, up-front about its creators' desperate need for attention. Give it an inch, and it takes a mile.