Question

Why hadn't Europeans used maritime routes before the age of exploration

Answer 1

They didn't have the ships and navigation skills to travel around Africa to Asia.

The Age of Exploration would not have been possible without the inventions of new ships like caravels or the extensive research/studying of navigation by individuals like Prince Henry the Navigator. These two factors allowed explorers to have a more reliable means of transportation and a better understanding of the geography/conditions they would face during their expeditions.