Most naturists would be horrified that you would think this - believe me, as practised in Europe, it is VERY un-sexual (hence the reason you will find very few teenagers in naturist camps!)
I am afraid that when we were younger we would drag our reluctant children to “clothing optional” beaches and although our seven-year old was a natural nudist (most kids of that age don’t know what clothes are for anyway!) the girls insisted on keeping their cardigans on at the beach. They now look back on it as a harmless eccentricity on their parents’ part.
Having said this, I’m surprised (@GalwayGirl) that your guest would want to practise nudity in your place if you don’t advertise as “clothing optional” as I’m sure he could find somewhere nearby to accommodate him or he could become a “textile” for a night! I should just say your elderly mother lives with you and she would be uncomfortable with his being naked in the common areas of the house. If he doesn’t understand this then I’m afraid he isn’t being sensitive to your wishes as a host and I don’t think you should accommodate him.