She started singing with this Big Band at 17 in 1939. Imdb quotes her as saying:
The happiest times in my life were the days when I was traveling with Les Brown and his band.
Performed by Doris Day with Les Brown and His Orchestra
Seriously, the most unusual thing about her is that she started in Hollywood films in her teens, and only became a huge star in her thirties, an age when most Hollywood starlets of the era saw their careers evaporate. And that's why the standard joke about her was "I knew Doris Day before she was a virgin!", bazinga!