Pedo = Child
Philia = Loving
In the modern context of english (what we're all using, asshole. I don't see you speaking ye olde vernacular) the Philia portion of Pedophilia means sexual attraction.
Ergo, in the modern language, pedophilia = child sexual-attraction.
Or do you mean prove it's a real thing? in that case we can assume someone is a child based on sexual maturity, and for ease let's focus on women.
Girls gain sexual maturity upon their first period, proving they can bear offspring. This happens during puberty, which is, on average, around the age of 11-13. Ergo; wanting a child younger than a preteen is, biologically speaking, pedophilia.
Now, culturally speaking, we have had established for nigh on 60-80 years that a girl shouldn't be fucked or lusted after until 18, after which they have gained a standard education and are expected to think for themselves. Until then, they are under the care of caregivers and they decide things.