Star Wars Episode III: Revenge of the Sith Chapter XII: Secret Assignment
At twenty-three years old, Anakin is the youngest Jedi to have served on the Jedi High Council. The novelization establishes that Mace Windu previously held that record, having joined at age twenty-eight, following his exploits against Gorm the Dissolver in the Arkanian Revolution. Master Yoda, on the other hand, is perhaps one of the oldest members appointed to the Council, having only earned the rank of Master after the start of his second century—as Yoda himself states when he tells Luke Skywalker he has trained Jedi for eight hundred of his nine-hundred-year lifespan in Episode V.
The fact that Palpatine knew Anakin wished to hold a seat on the Council, despite Skywalker not asking for this, is perhaps an indication that Palpatine has been gleaning knowledge of Anakin's thoughts and desires through the Force. He later reveals he has knowledge of Anakin's visions, and his fear for Padmé's life.
Palpatine has been serving as Supreme Chancellor for thirteen years now, after winning a second election in 28 BBY, and after his term was indefinately extended in the Chancellery election of 24 BBY for the duration of the Separatist crisis. This unconstitutional expansion was further solidified with the outbreak of the Clone Wars.