A qualification for a president under article 2 of the constitution is

Article II of the Constitution states that: 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.

So:

35 years of age is a qualification.