- Hermione: "It's not going to work... You see this? This is an Age Line. Dumbledore drew it himself...a genius like Dumbledore couldn't possibly be fooled by a dodge as pathetically dim-witted as an Ageing Potion."
- Fred: "Ah, but that's why it's so brilliant!"
- George: "Because it's so pathetically dim-witted."
- — Hermione Granger and Fred and George Weasley on the twins' attempt to fool the Age Line Spell[src]
The Age Line is a spell which creates a line that is impassable by people below or above a set age. The incantation is unknown.
It was used by Albus Dumbledore to stop underage students from placing their names into the Goblet of Fire as potential candidates for the Triwizard Tournament. Subjects who attempt to breach the line are repelled, and grow long, white beards, regardless of gender. The Age Line is impassable even by users of an Ageing Potion, which was proven when Fred and George Weasley attempted to bypass the Age Line to enter the Triwizard Tournament. Thus, it works for calendar age, not physical age. Others affected by the age line were Summers of Hufflepuff and S. Fawcett from Ravenclaw.