Ask yourself this question:
"Is it possible for me to become the president of a major country?"

Some would say no, that is illogical. From a realistic standpoint, the chances of being competent enough to become the president of a major country is very small, the chances of actually becoming one is next to nothing.
Some would say yes, if you are intelligent, have a good set of morals and a good sense of justice, and you REALLY put ALL of yourself into becoming the president of a major country, you may actually become one.

Do you think most of our current leaders would have said yes or no to this question at the age of 25?

I personally think yes. The power of optimism should not be overlooked. Most successful people have are positive about themselves and their capabilities. I think optimism has helped a lot of our world leaders, and rocketed them to believing they can reach their goals. Optimism definitely helped them and was a major contribution. Without it, these goals would not be reachable.