There’s a carve-out which allowed Washington et al. to qualify for President.
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. -- US Constitution, Article II, section 1, paragraph 5.
The provision of "or a Citizen of the United States, at the time of the Adoption of this Constitution" can be thought of as a kind of selvage, to use the textile/sewing/weaving term. It is the self-finished edge of Constitutional qualification for our nation's first generation of leaders.