And he was a subject of Great Britain.
The United States of America (and its Constitution, remember that?) did not officially exist until 1893.
I think you got some numbers transposed. I assume you meant 1783 when the Treaty of Paris was signed? Actually the country began existence July 4, 1776. That is even the date from whence early court cases counted citizenship as having began.
No person except a natural born citizen, or a citizen of the United States, at the time of the adoption of this Constitution, shall be eligible to the office of President; neither shall any person be eligible to that office who shall not have attained to the age of thirty five years, and been fourteen Years a resident within the United States.” ( Or a citizen of the United States at the Time of the adoption of this Constitution ) At the time of adoption of the Constitution? So yeah, I remember. You know, words do have meaning.