I don't draw it at age, I draw it at coercion. If someone is pressuring someone else into uploading nakes pics that's bad, age would just be an aggravating factor in the badness when deciding how much to punish.

While the idea of a six year old uploading naked pics makes me extremely uncomfortable I think that's a parenting issue (something has probably gone very wrong and that's what needs fixing, not the symptom of posting online), not something to be governed at the payment processor level.