Looking at Fred's and George's long, grizzled beards, Luna asked curiously, "You've already passed the Selection Examination, so how were you still stopped by the age limit?"
Vizet looked at the floor instead. Two parchment strips lay scattered there, with Fred's and George's names written on them, along with the school name, "Hogwarts";
Aside from that, there was also a small half-bottle of green potion lying on the floor.
There were many kinds of green potions, but paired with the parchment strips used for registration and Fred's and George's grizzled long beards, it was easy to tell that this was a bottle of Ageing Potion.
The key to Ageing Potion lay in Vintage Red Wine and tortoise shell. If explained through "marks," Ageing Potion needed to obtain the "vintage" of the Vintage Red Wine, as well as the tortoise's "experience";
The "vintage" and "experience" needed to correspond to each other. For example, if eight-year Vintage Red Wine was used, it needed to be paired with a tortoise shell from a tortoise around eight years old.
In addition to that, bat tongue, caterpillar pupa, and Essence of Dittany also had to be added;
Bats had a unique ability of "echolocation," so bat tongue could be used for "backtracking," ensuring that after the potion's effects wore off, the drinker could return to the age they ought to be;
Caterpillar pupa was similar to Death's-head Hawkmoth Pupa. The "transformation and rebirth" contained within could assist the bat tongue in "backtracking" the age;
After returning to the original age, the healing effects of Essence of Dittany could be used to repair the damage caused by changing age.
In truth, Fred and George's use of Ageing Potion did indeed have a chance of succeeding;
But they needed to carry out "ageing" with their entire body