Well, the opinion that a child can consent is technically acceptable, because the line at 12,13,14,16,18,21 years is arbitrarily drawn which is why it differs in various countries.

But in practice he should have used common sense and at least drawn his own line.

This charitable interpretation doesn’t make sense when you remember that he also says it’s a shame people can’t have sex with animals/their family pets. They definitely cannot consent, even if you argue that a 12 year old could (which I’d also disagree with).