Responses
I would not know. My sister was with a 17 year old when she was 12. Now they are married for many years and have 2 children. It depends from situation to situation. let's not forget that when puberty arrives we are no longer children and sexual impulses arrive for everyone. Let's not act stupid as if we hadn't been through that phase.
in any case we are talking about fiction here so we cannot make any comparison with reality. as with any other fictional product.
But genuine question, if you are in Yuu-nii's position, how do you properly reject this child's advances and make him properly understand the difference of their "likes"?