But if we have to pick an age, it should be the SAME as other adult responsibilities
Here in Israel not even all voting is on the same age limit—elections for government are from 18, and municipal elections are from 17.
Maybe not all other adult responsibilities—I can see a good argument for bringing on responsibilities slowly, with voting toward the end. But it’s really difficult to disallow voting on topics that affect earlier-granted responsibilities (cf US voting age reduction in response to military draft). Simultaneity solves that.
To the extent that voting matters, it should be done in a considered fashion by people who are able to apply long-term thinking. At the very least, by people who know they’re responsible for long-term outcomes, and know what that means. The best way to tell people that they’re making adult decisions and this is one, is to grant it similarly to other adult rights/responsibilities.
(aside: I’m somewhat amenable to the argument that voting exists only to pacify the electorate, so it should be granted to anyone who might otherwise revolt, and it’s a fine training ground for children’s future learning of responsibility. But that’s not my default position—I generally think that voting is an exercise of authority, not a practice for more important things).