"A boy of fifteen who is not a democrat is good for nothing, and he is no better who is a democrat at twenty."
, an American Founding Father, the principal author of the Declaration of Independence (1776) and the third President of the United States (1801–1809). At the beginning of the American Revolution, he served in the Continental Congress, representing Virginia and then served as a wartime Governor of Virginia (1779–1781). Just after the war ended, from mid-1784 Jefferson served as a diplomat, stationed in Paris. In May 1785, he became the United States Minister to France. Jefferson was the first United States Secretary of State (1790–1793) serving under President George Washington. With his close friend James Madison he organized the Democratic-Republican Party, and subsequently resigned from Washington’s cabinet. Elected Vice President in 1796, when he came in second to John Adams of the Federalists, Jefferson opposed Adams and with Madison secretly wrote the Kentucky and Virginia Resolutions, which attempted to nullify the Alien and Sedition Acts.
There is a detailed research on the origins of this quote worth reading here.