Studies showing most sexual relationships from ages 10-16 are consensual:
Condy Et Al: http://web.archive.org/web/20180527005054/http://sci-hub.tw/10.1007/bf01541421
Method of study is assessing randomly-picked college students recounting their experiences (Mostly when they were 12)
Arreola Et Al: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2865208/
Method of study is interviewing adults from bars across developed states in the US (Florida, Los Angeles, New York etc.), recounting sexual acts when they were underage
Stories of Underage Sex:
5-Year-Old Boy who masturbated a 17-Year-Old + 7-Year-Old Girl who had sexual relations with Janitor (In the ‘Boys and Men’ and ‘Girls and Men’ section respectively):
Articles on the mental development of a child and their ability to consent to sex:
Piaget’s Theory of Cognitive Development: https://www.verywellmind.com/piagets-stages-of-cognitive-development-2795457
From age 8 and above, logical thinking has developed and children are able to empathise
When Children Understand Consequences: https://judyarnall.com/2019/02/18/when-do-children-understand-consequences/
‘Children are able to begin understanding consequences around age 6 and are much better at it around age 13’