A presidential candidate must be a natural born citizen of the United States, a resident for 14 years, and 35 years of age or older. It usually takes Presidents 10 years to just make a name for themselves, gather money for their campaign and educate themselves in the political field. It all adds up and most candidates are in their 50s, 60s, and 70s. Even old Joe is pushing into his 80s.
Being the most powerful person in the US takes a lot of time so that's why they're all boomers.
