Ginny inconsistancy?

[amendels at lynx.neu.edu]

No: HPFGUIDX 28088

Hi I am new so this may have been covered before, but it wasn't in the FAQ. At the end of Chamber of Secerets, Ginny is upset 
because she thiks she will be expelled from Hogwarts and says she's been wanting to go ever since Bill started. given at least one 
year between siblings ( and in some cases we know that it was two), how old could she have been when bill started hogwarts, my 
rough calculations put it at one or two years old. (Please help me out if I am wrong.

Aurora