What were the main factors leading to the origin of the age of explorations?

Some major factors leading to the Age of Exploration were the rise of the Ottoman empire, improvements both in shipbuilding and navigational technology, and a desire for goods from the Orient—most importantly, spices. Exploration was also driven by religion: Marco Polo had recorded the desire of the Mongols to learn more about Christianity. European rulers remembered the Crusades, a historical precedent, if unsuccessful, for attempting to spread Christianity to other cultures. Marco Polo had also mentioned unknown lands, such as the island of Japan, that the Europeans became hungry to find and explore.
When the Ottoman Empire conquered Constantinople in 1453, it cut off Europeans from traditional trade routes to the East. North Africa was also controlled by Muslims who were in conflict with Spain and Portugal and blocked their access to southern trade routes. Land routes were available but both dangers from bandits and the high tariffs paid to cross them made these routes unprofitable. Yet Europeans were desperate for spices, which they used for medicinal purposes as well as to flavor foods. This pushed them to find alternative routes.
A growing Renaissance consensus that the earth was round rather than flat inspired people to abandon their fears of sailing off the edge of the earth. Further, the Portuguese developed a more navigable sailing ship called the caravel, which allowed sailors to more safely travel longer distances (sea travel was still by no means safe, but safer). The Portuguese also began building bigger merchant ships armed with cannons meant to deter pirates. The Portuguese had already done a good deal of sea exploration, so they had some idea where to head when they finally made it around the Horn of Africa and to India. When they arrived in India they could buy many desired spices, and sell them at a huge profit.
Desire for profit was the biggest motivation behind exploration. Europeans realized there was a vast world outside of Europe, full of gold and other natural resources that could bring in immense wealth. As explorers such as Vasco da Gama and Magellan made successful voyages, European leaders became wildly interested in the profits to be gained from exploring uncharted lands.
Additionally, improvements in navigational technology, such as in the compass and the invention of the astrolabe, aided travel. Being cut off by the Ottoman Empire, improvements in sailing vessels, a desire to spread Christianity, and the desire for wealth drove Europeans to take on the very risky venture of exploration.