Hugh Jackman and Dannii Minogue are among 70 stars to lend their voices to a new book called Dear Me: More Letters to my Sixteen-Year-Old Self .
"There will be a time when you get over Penny dumping you at the bus stop," 43-year-old Hugh Jackman writes to his 16-year-old self in the book. "In fact you'll see her in a couple of years and wonder why you cried every time you heard the Lionel Richie song 'Penny Lover'."
He adds, "Oh and the patch of zits on your forehead will also go but probably not as quickly as you hope. PS: buy shares in Google when they're invented."
Meanwhile, Dannii Minogue tells her younger self, "On a trip to Ibiza you will meet your true love in a nightclub. I know... tacky... but you can never plan these things.
"Deny, deny, deny if you are asked about how much hairspray you have used... your hairdos may be responsible for part of the hole in the ozone layer."
Rocker Alice Cooper advises his teenage self, "'Trashy girls are exciting for about five minutes. Keep your eye out for a really good lookin' church girl. Then you'll have the best of both worlds."
And Harry Potter author JK Rowling suggests, "Don't have your ears pierced by a hippy at a music festival. That was one nasty infection. Avoid bass players. All of them."
Check out some more stars back when they were teenagers in our before they were famous gallery...