I think a better translation for "impune al ridiculo" would be "immune to ridicule".
So then you are saying that older people (like you) are immune to ridicule and can write anything providing you do not offend anyone.
Did you? = Sabia Ud.?
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Did you know that people older than 70 years (like me) are "away with the ridiculous" and can write anything as long as you do not offend anyone! = Sabia Ud. que las personas mayores de 70 años (como yo) estan "impune al ridiculo" y pueden escribir cualquier cosa, siempre y cuando no ofendan a nadie!