Young Tywin Lannister (in Pascali's Island)
Yep, that's Lannister patriarch Charles Dance - in total young stud mode - hanging out with young Helen Mirren. Old people! They used to be young!
Young Ned Stark (in The Bill)
Old age is coming.
Young Cersei (in The Jungle Book)
It's just a little bit weird to see Lena Headey younger, without blonde hair, and also not having an incestual affair with her brother.
Young Tyrion Lannister (in The Station Agent)
I've seen Peter Dinklage in X-Men: Days of Future Past (which takes place in the 70s) and he looks pretty much the same. Dude ages WELL.
Young Olenna Tyrell (in The Avengers)
Not THAT Avengers - the TV show with British people. Although weirdly Diana Rigg IS playing Black Widow here.
Young Littlefinger (in Queer as Folk)
Youthful Aidan Gillen, livin' up the queer lifestyle with Jax from Sons of Anarchy.
Young Catelyn Stark (in Hidden Agenda)
Michelle Fairley - always hard-edged, beautiful, and probably a lot of fun at weddings.
Young Joffrey Baratheon (in Batman Begins)
"Thanks for the help, Batman! I too will now become a violent sociopath."
Young Theon Greyjoy (in Equus)
Back when Alfie Allen was mostly just Lily Allen's little brother.
Young Sandor Clegane aka The Hound (in The Book Group)
Note the unburned face, lack fo armor, and not murdering everyone.
Young Davos Seaworth (in A Little Princess)
Liam Cunningham used to be a STUN-ion knight.
Young Robert Baratheon (in The Full Monty)
Note: he also played Fred Flintstone in Viva Rock Vegas.
Young Stannis Baratheon (in Welcome to Sarajevo)
Stephen Dillane, you probably won't win the Iron Throne - but you've won our hearts.
Young Jorah Mormont (in Mountains of the Moon)
Iain Glen didn't ALWAYS serve Khaleesi.
Young Hodor (in life)
Before Game of Thrones, Kristian Nairn didn't do much acting - too busy being a DJ and - ironically - saying his own name over and over.