They were nearly all young men in 1776

From The Jefferson Lecture by David McCullough, delivered in 2003.

They were nearly all young men in 1776, it should be remembered, young men who believed, as Thomas Paine proclaimed, that the birth of a new world was at hand.

Jefferson was thirty-three, Adams, forty, Benjamin Rush, the Philadelphia physician, was all of thirty when he signed the Declaration of Independence. Rush, one of the most interesting of them all, was a leader in the anti-slavery movement, a leader in prescribing humane treatment for the insane, and the first to champion the elective system in higher education.

When George Washington took command of the army, he was forty-three. He had never led an army in battle before in his life, any more than the others had had prior experience as revolutionaries or nation builders.