What year are the Weasley twins in when Harry Potter arrives?

Fred and George are in their 3rd and 13 years of in the first book. I can't remember what page it on but it says so specifically in the book. If you go on Rowling website it will tell you that you can't go to Hogwarts until your 11 a href="http://www.jkrowling.com/textonly/en/faq_view.cfm?id=90" rel="nofollow"http://www.jkrowling.com/textonly/en/faq…/a so by logic they're 13 at the being of the book and on her website it also says that they're birthday is on April fools day a href="http://www.jkrowling.com/textonly/en/extrastuff_view.cfm?id=7" rel="nofollow"http://www.jkrowling.com/textonly/en/ext…/a .