"An Age Line! ...Well, that should be fooled by an Aging Potion, shouldn't it? And once your name's in that goblet, you're laughing - it can't tell whether you're seventeen or not!"
-- Fred Weasley, wrong about the Age Line (GF16)
Ageing Potion causes the person drinking it to grow older. The more one drinks, the more one ages.
References from the canon
Fred Weasley, George Weasley, and Lee Jordan took a few drops of Ageing Potion in an attempt to fool the Age Line around the Goblet of Fire into thinking that they were a few months older. The Line wasn't fooled. They were thrown back out of the circle, then sprouted full beards (GF12).
NOTE: In the US editions, this name of this potion is spelled 'Aging'.
From the Web
"Ageing Potion" from Harry Potter Wiki