The Rolling Stones released the studio album Beggars Banquet in December 1968. The eight song in it (the third track on side two), “Stray Cat Blues,” was written by Mick Jagger and Keith Richards. In it, the singer lusts for sex with a groupie aged 15 years, which illegal in both the UK and the USA. He describes the young girl as a ‘stray cat’ who isn’t shy about performing sexual acts.

I give the song video from the Rolling Stones’ YouTube channel:

Here are the lyrics from Genius:

Stray Cat Blues
by Mick Jagger and Keith Richards

Ah… hey
Yeah, got some tail

I hear the click-clack of your feet on the stairs
I know you’re no scare-eyed honey
There’ll be a feast if you just come upstairs, but
It’s no hanging matter
It’s no capital crime

I can see that you’re fifteen years old
No, I don’t want your ID
And I can see that you’re so far from home but
That’s no hanging matter
It’s no capital crime

Oh yeah, you’re a strange stray cat
Oh yeah, don’t you scratch like that
Oh yeah, you’re a strange stray cat
I bet, bet your mama don’t know you scream like that
I bet your mother don’t know you can spit like that

You look so weird, and you’re so far from home
Bet you don’t really miss your mother
You look so scared I’m not no mad-brained bear
But, but it’s no hanging matter
It’s no capital crime

Oh, yeah
Woo!
I bet your mama don’t know that you scratch like that
I bet she don’t know you can bite like that

You say you got a friend, that she’s wilder than you
Why don’t you bring her upstairs?
If she’s so wild, then she can join in too
It’s no hanging matter
It’s no capital crime

Oh yeah, you’re a strange stray cat
Oh yeah, don’t you scratch like that
Oh yeah, you’re a strange stray cat
I bet your mama don’t know you can bite like that
I’ll bet she never saw you scratch my back

According to Songfact:

In the lyrics, the girl in the Beggar’s Banquet version is 15 (“I can see that you’re fifteen years old”). However, on their 1969 USA tour and subsequent ones, Mick Jagger reduced the age of the girl to 13. He wanted to test public opinion to the limit.

Indeed, the song is included in the live album Get Yer Ya-Ya’s Out!: The Rolling Stones in Concert, released in September 1970, and one can hear “thirteen years old” in the video from the Rolling Stones’ YouTube channel:

Otherwise, Mick Jagger would often change it to “sixteen years old,” the legal age in the UK.

In fact, the girl in the song is probably a young groupie. Tom Taylor writes in Far Out Magazine on May 25, 2021

Devon Wilson, who was a groupie of the time and reportedly had relations with Mick Jagger, told David Henderson in the book ‘Scuse Me While I Kiss The Sky: “You know the song, ‘Stray Cat Blues’? [Jagger] told me he wrote it about a certain chick. He said he usually doesn’t write like that, but he had this one particular lady in mind. When he was in California the girl called him and said, ‘Thanks for writing that song about me’. He was shocked because he didn’t think she could have recognised herself. But she did and it completely freaked him.”