Here is an exchange I saw in a WeChat group today:
A： 谢谢您，李老！ 【抱拳】【抱拳】
B： 谢谢您，老李！ 【偷笑】
I'm fairly familiar with the usage 老X as a term of address. And I gather that X老 is a much more respectful term. I guess my question is, when would I ever actually use X老? I seem to recall hearing a story a long time ago about a foreigner trying to use X老, but the old man being addressed was "too young" and the effect was awkward.