In Article II, section 1 of the Constitution, it says 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."
As for why the Founders put forth some rules about who could be president, it is probably because they knew they were creating the most important position in our new government. This position was unlike a monarchy, which was inherited; the new president would be democratically elected, so the Founders believed it was important to make sure his first loyalty was to America. That is why they preferred to have a president who was born here and raised here, rather than someone who came here from England (or Another Country) and might be more loyal to that place than to the United States. As for the age requirement, perhaps this was because 35 was seen as "middle age" back then, a time when one was neither too young nor too old, and had become sufficiently mature to govern a country.
Chat with our AI personalities
The people who wrote the Constitution did not want the president to be able to create law and so go above the law . They wanted a president who, although given a lost of power, was forced to obey the law already established when he took office. The idea is called the separation of powers. The power to change the law is given to Congress which is totally separate from the presidential powers.
They had just emerged from a war against Great Britain, and wanted to avoid vesting too much power in one person like the British did with their king at the time.