Why is the age of consent different in different countries?

Anonymous
Why is the age of consent different in different countries?
As I understand, the age of consent would be the age someone is old enough to understand the consequences of having sex.
The age of consent in the Philippines is 12.
The age of consent in Bahrain is 21.
The age of consent in South Korea is 20.
The age of consent in the UK is 16.
The age of consent in Brazil is 14.
The age of consent in Nigeria is 11.
There are petitions online you can sign to change the age of consent from 11 to 18. Clearly, people think this is wrong as do I, but I don't understand why there isn't a universal age of consent and why all these countries have different ones?
Why is the age of consent different in different countries?
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