Dear 100 Hour Board,
Is there an objective age of consent? That is, independent of laws, customs and culture, does such a thing exist in the eyes of God, and at what age would it be?
No. God deals with us on an individual basis. It's humans who have the need for general bars that apply to all people.
I recognize that there are some objective truths that apply to all humans ever (like, don't rebel against God) but that number is incredibly low. Even mandates such as not killing other people are sometimes meant to be broken (think Nephi and Laban). General rules of thumb are nice for people, because there's just no way we can know all the possibly information behind every situation, and we don't have the authority to proclaim what is right and what is wrong. God doesn't have those problems. And so if there is anything which could conceivably have an exception, there isn't going to be some objective, strict standard God holds us to. And I can think of a heck of a lot of potential exceptions to age of consent (think mentally handicapped people, for one).