It would depend whether you were born in the first or second half of 1990. As the cut off point for acceptence into school is some time in the summer, each year has a mixture of people that were born in one year (eg from summer 1990 to end of december 1990 and from jan 1991 to summer 1991)
So if you were born in the first half of the year (Jan-summer 1990) you would have been with people who were born from summer 1989-summer 1990 and you would have left school in 2006.
If you were born in the second half of the year (summer 1990-december 1990) you will have been in the next year down, along with people who were born from summer 1990-summer 1991 and would have left school in 2007