Actually there is. mens rea means the ability to cognate the commission of the crime. And under normal law this requires one to be 100% legally competent (an insane person cannot form this mens rea because of mental impairment). A minor cannot be legally competent - and for good reason, their brains simply are not fully physically developed

but the plain fact remains that any 13-year-old without a severe mental disability is perfectly capable of understanding what a rape or murder is, how society views such acts, and why they are wrong

Simply biologically FALSE. And you cannot marshall ANY actual FACTUAL evidence to support your claim.