Here's another thought...
Biologist that I am... I've read that the transition from childhood to adulthood is more than just going through puberty. Neurologists have claimed the brain is undergoing maturity and changes (physical changes) in the "growing up" years, and the brain's physical transformation isn't complete until about age 25!
This partially explains why such a high percentage of marriages fail, especially among the young. Recall how divorced will often say, "we became different people... we just drifted apart"? I submit that they got married too young... because they were "in love", of course... were not "on the same page from the get-go" with their adult issues but didn't know it at the time.
IOW... when you're 18, you haven't yet had time to even form your opinions/thoughts/feelings about the majority of life's "adult issues", and therefore you're not mature enough to be entrusted with something so important as the vote.
Remember when you were a teen and thought you had it all figured out? Then as you got older you realized how little you really understood? The teen years can be tumultuous not only for teens but for their parents... but it's understandable
I agree. 18 yr olds should NOT be allowed to vote.
This jibes with my theory that we humans (at least we North American, first-world humans) have two chronological lifetimes - the first from birth to 16, and the second from 16 to death. Being 16 is equivalent to being a "newborn" adult. 17 = 1, 18 = 2, etc.
In my experience, I "woke up" at age 7, in that I started remembering everything, started acquiring my childhood hobbies and interests, etc. My life wasn't just a blur anymore. Likewise, I do not think it's unreasonable to believe that a lot of us "woke up" around age 23. As in, stop acting like a dumbfuck and start getting serious about things. Paying attention. Striving to make good decisions based on considerations 2 moves beyond the immediate reaction, etc.
Not a hard and fast rule, but an observation...