expiration age in AI Stimulus

Dear all Game makers
I have a question about AI stimulus
I know that the “age” indicates the time left after the bot last sensed. But I tried to print “expiration age” and nothing meaningful showed up!! the question is What exactly this parameter is?
(I could not find anything in the Doc or Forums)

Its been almost 6 years so I doubt you still need this, but for future developers - Expiration Age is how long it will take before the stimulus expires. Usually, the same thing as your AI perception’s Max age.