He was born on April 18, 1971, and the Harry Potter and the Goblet of Fire movie came out in late 2005, so he was around 34 at the time. See the Related Link below for his imdb (Internet Movie DataBase) entry.
Harry Potter is a fictional character....do you mean Daniel Radcliffe who plays him in the films? If so think they are both equally as good, though, David Tennant is a much more versatile actor as he...
It depends on the book. In each book, his age increases by 1. He starts out 11 in the book 'The Philosopher's Stone' and to the seventh book 'The Deathly Hallows', he's 17.