The character is a military man, well travelled and modern-minded, but his father is a very old-school Welsh nobleman and the character's education on social etiquette took place in the early 20th century, so it is probably pretty traditional. Thanks to Jane Austen, I am aware that the gentleman would make a bow to the lady in the 18th century (shake hands with more intimate acquaintances), and I have the idea that the hand kiss was common in Victorian times, but I didn't find anything on its status in the Edwardian and post-Edwardian period.
I tried googling "1930s", "Edwardian", "social codes", "etiquette", and "hand kiss" in all possible variations, but I guess the question is too specific to find the right answer if you don't know where to look.
