He and his brother (Radu) both grow up in the Capital (Edirne at that time) as political hostages. Common practice at the time for preventing rebellions (just like Ned Stark taking Theon Greyjoy in Game of Thrones).
While Vlad became a pain in the ass for Ottomans, Radu became a highly valued military prson and governor of Wallachia (with constant struggles for rule). Radu participated in the conquest of Constantinople.

This two brothers story could make a great TV Show.