Rufus Wainwright - at 14, his song in Tommy Tricker and the Stamp Traveller earned him a Genie nomination.
Camille Saint-Saens gave his first piano recital at the remarkable age of 5. I remember reading the Beethoven sonatas story in a biography of Fauré.
Neal Schon was recruited to be Carlos Santana other guitarist when he was 15.
“**Kid” Jonny Lang **and **Joe Bonamassa **and **Kenny Wayne Shepherd **were all standouts from a Blues perspective in their teens.
How old was George Harrison when the Beatles broke in the UK? Hmm, born in '43 and their first hit was in '62, I think - so 19, not 18…
The first performer that came to my mind was violin prodigy Vanessa Mae (although her professional debut at age 10 makes her practically a senior citizen compared to the artists you cite). However, to make up for her late start, she’s insanely rich due to concert and CD sales.
Shuggie Otis had released two solo albums before his eighteenth birthday, as well as being featured on the album Kooper Session and playing on a variety of other artists’ records including Frank Zappa’s Hot Rats. His second album included the self-penned single “Strawberry Letter #23” which later became a big hit for the Brothers Johnson.
Robin and Maurice Gibb of the Bee Gees were still 17 when “Spicks and Specks” (the Bee Gees’ 12th single) became a #1 hit in Australia.
Several members of the Cowsills were under 18 (as young as 11, I believe) at the time of their first big hit, “The Rain, The Park and Other Things”.
Yeah, I have his CD Inspiration Information - very insider-music-snob stuff to reference, but actually a cool, good album worth listening to. The whole problem of him going a little nuts and dropping out of the scene is what really prevented him from becoming an all-in-one threat a la Stevie Wonder and Prince…
Same guy and song I thought of.
As has been said, it is difficult to define “hit” for classical composers. But Mozart and his older sister Nannerl were traveling to places like Italy and England when his was six.
Apparently at the time child prodigies in such things as music, speaking different languages, memorizing books, was a rage in Europe at the time.
More of a sideman and loose on definition of hit but Craig Chaucico of Jefferson Starship fame was recording with Paul Kantner and Grace Slick on albums such as “Sunfighter” when he was 16
Donny Osmond (with The Osmonds)
Menudo
Ya.
See post number 1 and post number 11? 
I wouldn’t count this. “Valley Girl” is really a Frank Zappa song, with music and most of the lyrics written & performed by dad. Moon Unit only did a guest stint.
Petula Clarke is best known in the U.S. for “Downtown” (recorded when she was about 32), but she had already been a famous performer in Britain (and most of Europe) since WW2, when she was 12 years old.
Connie Francis began recording when she was 13, although she didn’t have a hit until she was 17.
Peggy March was only 14 when she recorded “I Will Follow Him” and had just turned 15 when the song hit #1.
Annabella Lwin of Bow Wow Wow was 14 when “Go Wild in the Country” and “I Want Candy” were released. Imagine doing a nostalgia tour in your early 30s. That’s what she did in the late 90s!
Bad4Good, if you were to call them successful. Featured Thomas McRocklin, who is a phenomenal guitarist (and appeared in Steve Vai’s The Auidence Is Listening). Lead Vocalist was Danny Cooksey, who started out as Sam on Diff’rent Strokes. and was later Montana Max on Tiny Toons.
Can anyone find a link to the “Icelandic” hit Bjork recorded when she was eleven?
Picky, Picky, Picky 
You earn my hatred for the day. This was a local dance hit, and I had to endure it for a couple of months on the radio and in clubs. It mercifully disappeared, and I sincerely couldn’t remember who the singer had been, nor what the song had been, until your post. Crap. Now I’m remembering snippets and looking up the video and MP3 despite hating the song.
I’ll be okay, though; invariably someone will “reminisce” about LaTour’s “People Are Still Having Sex” from roughly the same timeframe, and I can forget about Jordy…
Thunderclap Newman’s guitarist Jimmy McCulloch was 15 when they had their only hit “Something in the Air” in 1969.
[Quote=Wikipedia]
Thanks to “Something In The Air”, McCulloch is the youngest person to date to have performed on a number one hit song in the U.K.
[/Quote]