Why not a 15 year old script kiddie? All you need to coordinate this attack is some anonymous server power that cannot be linked to you, and it's not something that's very hard to come by.
Depends on how weak the keys are. They say some were trivial, but it's possible others still had enough entropy to require a lot of brute forcing. Most 15-year-olds don't have a lot of capital to deploy.
Yeah, but this one, if he exists, does. Crack open a piggy bank, find enough money to buy safecracking tools.
Yeah.... if the first ones were trivial and acted as a proof of concept, that would generate enough money for them to invest in better servers with more distance from the actual person running it.