Answer
Alexander Nevsky was only 19 years old when he first became the Prince of Novgorod. This appointment happened at a critical time for Novgorod, as the city faced threats from both internal conflicts and external invasions. Nevsky's leadership and military prowess proved instrumental in safeguarding Novgorod's interests, including the famous defeat of the Swedes in the Battle of the Neva in 1240, earning him the title "Nevsky."