An inch or two would be adequate. He can squeeze into it now on the last holes in the buckles, but it isn't comfy or a good look. I could hardly sleep last night for thinking about the difficulties in letting out his kilt. I was wondering if there's such a thing as extensions for the buckles, or maybe just new buckles that are longer. But I don't know if that would make it fit oddly.
Thanks for the welcome and for the reassuring words.