Bill is starting his third year.
Rowling's statements about the ages of the Weasley children, particularly Charlie, seem at first glance to be contradictory. However, Philip Legge has written a brilliant analysis of all the related canon information and come to the conclusion that for Rowling's statements to be true, Charlie Weasley must have left Hogwarts in his 6th year to go study dragons in Romania. Legge's essay, "Quidditch Through the (Weasleys’) Ages," is found here on the Lexicon.
Because this is the only way to rectify all canon statements, the Lexicon uses this logic to determine the years of Charlie's timeline.