In most depictions of David that have been painted and sculpted throughout history, artists opt to portray him as a young boy. They also commonly choose to capture the moment after he has slain Goliath. This approach is evident in well-known works by Caravaggio and Donatello.
Michelangelo, however, curiously decided to depict David as a young man. He also creatively chose to show him in the minutes before his battle, with a sling in his hand and a look of determination on his face.
At 17-feet tall, David is clearly a larger-than-life portrayal. Given the relatively realistic scales of Michelangelo's other sculptures, like his Dying Slave (7 feet tall) and his Pietà (5.7 feet), why is David so tall?
Likely, the sculpture's stature is a result of its intended location: the roof of the cathedral. In order for the public to fully appreciate the sky-high figure, it would need to be large enough to view from the Piazza del Duomo, hence David‘s colossal size.