Respectfully, I disagree with that card. Military service and being the President of the United States are not the same thing and it doesn’t make sense that their qualifications should necessarily be the same just because they’re important roles or because one can affect the other.
There’s no single age when a person goes from being unqualified for all regulated privileges and responsibilities to qualified. We let kids work at 15 before they can vote on labor laws and practices that may affect them, and (varying by state) they can drive before they can vote on traffic laws or serve as the highway patrolman enforcing them.
So even at an individual level, if we threw out the differences in maturity between this 18 year old and that one, I think it would be foolish to say 18 (or 16, or 21, or 35) is the age when someone goes from being incapable of any of these responsibilities to equipped for all of them.
I’m not here to tell you any of the above examples are inarguably the correct ages. I could probably be persuaded that 30 is old enough or President. I could probably be persuaded that there should be a maximum age limit too.
I like that 35 broadly means someone will reach a level of physical and mental maturity, and to the extent an age limit can affect this, probably have some meaningful measure of life experience outside of their education. I don’t think that means 35 is the indisputably correct age for the job, but you’d need me to convince your alternative still does a reasonably good job of limiting the pool of candidates to that group (so like I said, I could probably be convinced 30 is fine, 18 would be a very hard sell).
I don’t think something is right just because it’s the way things have been done, but I also don’t think we should move the age capriciously. We should look at the restriction and be sure it’s not unjust (and I don’t think a higher age for the President than for military service is unjust, as an example), and we should look to health and science evidence for how we mature biologically and mentally, and make an informed decision if either shows 35 might be too old (or too young!).
Okay, but, so what? Point to any age where you won’t be able to find examples of talented individuals who just missed the cut-off. This line of thinking can only be a rationale for removing the age restriction entirely, which I’m flatly against. You can’t use this as an appeal that the age should be Y instead of X. If we had some sci-fi/magic machine we could plug someone into that provided an objective and incontrovertible “maturity measure”, that’d be great and Beto could’ve run at 27 and Trump would’ve been ineligible at any age. But instead we have age, so we try to pick a safe compromise and we live with the fact that all age limits will be somewhat arbitrary.
These are the best arguments I’ve seen for lowering the age.