How can you just blatantly state "Yeah this culture is just wrong because I've determined that they are"? They could feel the same way about how we behave.

I agree with you on the taboo aspect. I'm 23 and personally don't think I could date anyone under the age of 21 (maybe a 20 year old if we clicked real well)

If you really want to look back at it, both men and women are reproductively viable once they've hit puberty, and that's likely what some of those lower consenting age cultures base their numbers off of. Personally I disagree with it because at that age everyone is a hormonal mess and is still developing mentally. However, since this is a subjective topic there's no way to objectively state they're wrong. (Unless there's a study out there that observed negative impacts on well-being for societies that engage in sexual activity at a younger age - then I guess yeah, you could definitely say their cultures are wrong)

We've created a consenting age of 18 because that's when someone is legally defined as an adult. Maybe I'm uneducated, but I don't think anything physically happens to anyone at the age of 18. Why do we not consider 25 to be the age of adulthood, as that's the average age at which the human brain stops developing entirely? If we did, would we see anyone under the age of 25 as unacceptable as well?