It’s because of the constitution. The most fundamental laws of the land are expressed in the constitution, and nothing else can override them. In the US, the 26

It’s because of the constitution. The most fundamental laws of the land are expressed in the constitution, and nothing else can override them. In the US, the 26th amendment establishes the minimum age of 18 for voting (https://en.wikipedia.org/wiki/Twenty-sixth_Amendment_to_the_United_States_Constitution https://en.wikipedia.org/wiki/Twenty-sixth_Amendment_to_the_...) and Article II, Section 1, Clause 5 of the constitution establishes the age of 35 for presidency. However, a constitutional amendment (which is difficult to pass with today’s political divide) could theoretically change that.