I can't think of a single place where it's legal for a motorcycle to go 90mph, other than a dirtbike race.
The Autobahn.
I'm actually not being flippant. There's no actual mandated speed limit on the Autobahn (at least in portions of the Autobahn). Now, I doubt he was actually on the autobahn unless he's an American who has decided not to use KPH. Which thus means he was doing it illegally or somewhere on private property.