Hi! Thank you for writing such a thought-provoking piece. I wish I could advise you in how to respond to your brother, but living in the UK, with such different rules and laws, I don't feel that I am able to look at your problem fairly.
But I too have a younger sibling- and all I can say it the fact that you are absolutely on the right track - you are considering your brother's purity and innocence in how you reply, and wish to ensure that your protect him, as I would with my little sister.
Be sure to be truthful - for whatever answer you give him will undoubtedly be met with a thousand more questions. But your little brother will grow into a man, and your answers now may shape a life which strives to change the laws and rules he discussed with his big sister all those years ago.
E x
Thanks for reading and helping