All because someone in the studio's wife had a southern accent. Nicks misheard "age of seventeen" and the song became about that couple.
After she had begun writing the song though, the band member's uncle John, and John Lennon both died in the same week. Or possibly her own uncle Bill was the deceased relative. Both stories have gotten around. Either way, the song transformed to a song about mortality. I really like the line "the clouds never expect it when it rains". That's just a great thought. She's got a serious voice, and her background singers know how to support her without masking her. She does make some odd choices, the long drawn out woo-ooo-ooo-unnngnna from 3:10 to 3:15 is almost disturbing when taking the song in context about death.
The group backing her up in the studio is made up of some great session players. The drummer and bass player each played with a who's who of 70s and 80s greats. Piano player Benmont Tench, who gives the song it's stage presence, is a founding member of Tom Petty and the Heartbreakers as well as a session player. The backup singers on this track are the same ones that still tour with her today. Producer Jimmy Iovine produced tracks for the Heartbreakers, Lennon, and U2 before founding Interscope Records, which he is chairman of still today.
Special note has to go to the guitar riff chugging on during the whole song. It's played by Waddy Watchel, who has played on more albums that I can list. It's the reason the song rocks in my opinion. 3 chords, all 16th notes, and it doesn't stop. Destiny's Child took it for their song Bootylicious, and Ms. Nicks gets a cameo in the video. Without that riff the song would just be another Stevie Nicks ballad; Waddy makes it rock.