It didn't start as anything anti-pedo exactly but there was a big move to increase the AOC in late 19th century, while it was mostly about prostitution, venereal disease, and I think "protecting" the virginity of young girls from wealthy families too - that move spread to other English-speaking countries, and in my view the higher AOC eventually lead to this view that was it was "wrong" to have sex those below the AOC, fueling anti-pedo sentiment. Until that time the AOC was around 10-12 for all of recorded history. Incidentally, these older legal codes seemed to focus on penetration and nothing else.