Underage Wizardry - the twins

[Marissa]

No: HPFGUIDX 130321

> Sherry:
> The twins would have turned 17 in April of GOF.  I believe 
> they even say that when the age restriction for the triwizard 
> tournament is announced.  WW kids are of age at 17 and 
> therefore, they would be able to use magic whenever they 
> choose. <snip>


Marissa: Actually, I always wondered about Fred and George and their 
experimenting, not their apparating which as Sherry points out they 
were old enough to do. They seemed to be using magic to create 
Weasley's Wizard Wheezes.
 
"We've been hearing explosions out of their room for ages, but we 
never thought they were actually making things,' said Ginny, 'we 
thought they just liked the noise." -GoF They weren't 17 in the 
fourth book, and Ginny says "for ages" so it obviously had been for 
a few years.

Does creating potions or their inventions not count as magic? And 
even if it can't be detected, wouldn't they still have to use their 
wands to create ton-tongue toffees and canary creams?  Maybe because 
there is so much magic in the Weasley house already what they're 
doing can't be detected. Anyone have ideas on this?