Showing a dog leadership is a lifetime commitment, 24 hours a day, 7 days a week. It is not training, it's a lifestyle when living with a dog. You can lose your position at any time, at any age. A dog is constantly looking for the strongest being in the home to be leader.
Instinct tells him that the packs life depends on it. In the wild when a pack leader gets old or sick another dog will take over as leader. This can happen at any time, at any age. The strongest beings are the leaders. That being said, if you have lost your leadership position or never had it in the first position, you can gain it back if you change your ways.