We do not pronounce 's' or 'x' sounds at the end of a word when the word is read on its own. But if it is followed by another word starting with a vowel (or 'h'), we generally pronounce 's' or 'x', i.e. aux Etats-Unis.
However, many times I encounter with counter-examples. One is below:
Les ados aiment cette nouvelle série.
Here, although both are followed by a vowel, we pronounce the 's' in 'Les', but not the one in 'ados'. So, is there a general rule about pronouncing (or not pronouncing) these silent letters when followed by a word starting with a vowel? Also, what would be the reaction of a native speaker for someone pronouncing 's' in every such situation? Thank you.