What is the difference between 老X and X老 as a term of address? Here is an exchange I saw in a WeChat group today:

李xx： 请大家为28号投票！
A： 谢谢您，李老！ 【抱拳】【抱拳】
B： 谢谢您，老李！ 【偷笑】
A： “李老”是尊称，“老李”是称呼！
C： 【强】


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.

Related questions:


&quot;小王&quot; 和 &quot;老王&quot; how to determine which to use?
What is a good form of address for a male friend who is too old to be 小, too young to be 老, and too humble to be called 大?
What is the polite/proper way to address elderly whom I am not familiar with?
Here's an explanation: In the case of people with good moral standing and high reputation (德高望重), you can add 老 after their surname, this is a very respectful (很恭敬的) address.

Screenshot from a book on Google Books. The relevant, very short sentence touching your question is highlighted (sorry, not very professional, but legible). 



Here's another source explaining this (mentioning scientists, statesmen, old teachers as the circle to whom you can apply this): 


  对德高望重的老科学家、老政治家、老教育家、老文学家，可以在姓之后加“老”字，以表示尊重。如“郭老”、“‘钱老”、“徐老”。