Was each time a different religious organization and did they require a baptism into their religion specifically?
I was raised and baptized into one flavor of Christian. They taught baptism in any other flavor of Christian was all good, no need to be baptized again to switch churches though the pastor might want to say an extra conversion prayer.
If I could wave a wand and fix something about voting in the US, it would be to improve access for already qualified voters.
Kids would vote similarly to their parents in general, so lowering the age means people from groups/locations that have good access would have more votes (not a bad thing) but groups/locations with poor access would still have poor access, possibly even worse access because of the increase in voters. So yeah, fix access first or it only exacerbates what I consider to be a larger issue in need of addressing.
Assuming good access to voting though, 18 makes sense to me as the time a person is an adult and legally responsible for themselves. I would be open to arguments for younger, it’s just not something I ever felt passionate about, even when I was under 18 years old.