You should be old enough to have real experience, but young enough to still be living with the consequences of the decisions you make. Right now there is a floor but no ceiling, and the results are visible.
You can't run for the House of Representatives before age 25 or the Senate until 30. The Constitution sets 35 for the presidency. The point is not to exclude anyone arbitrarily but to ensure that the people making decisions about the country have enough life behind them to understand what those decisions cost.
On the other end: if you are retirement age (65) or older, you should not be running for a position whose full term extends years beyond when most Americans have left the workforce. The job requires energy, engagement, and a stake in the future you are shaping. That is not a slight and it's not ageist. Enjoy your retirement!
This is a floor and a ceiling that gives plenty of decades to make a difference in public office.