GAZA, Oct 6 (Reuters) - "Freedom for Palestine!" chants 9-year-old Ahmad Abu Sharia in a Gaza Strip refugee camp, as he listens to a small radio bringing news of Israeli air strikes. "I want to become a commander in al-Aqsa," he says, referring to one of the main Palestinian militant groups, al-Aqsa Martyrs Brigades. Abu Sharia's dream of fighting Israel and perhaps achieving fame as a "martyr" is one shared by many of his friends and other youngsters in the Gaza Strip, a militant stronghold in an uprising against Israel since 2000. But Israeli troops left the territory last month...