Szia Robert! I'm a native Hungarian speaker, and I'd be more than glad to help you with your studies.

Though the explanations of Adam and Jonathan are both spot on, if you don't mind, I'd also put in my two cents. This meaning of the word 'gun' in Australian English comes from 'gun shearer', a term referring to a shearer in Australia who was excellent at his/her profession. It seems that over time, the 'shearer' part was dropped, and only the word 'gun' remained from the original term, which came to be used to describe anyone—not just a shearer—who was excellent, outstanding, at the top of their game, etc. As for the Guardian, although it is based in the UK, it still covers a lot that happens in other countries, including Australia, which is also a member of the Commonwealth of Nations. Also, when in doubt about the meaning of a word, I highly recommend the website Wiktionary. It has a lot of entries with etymologies for common words and phrases, and even colloquialisms and regionalisms which are mostly used in certain varieties and/or dialects of English spoken within the English-speaking world: https://en.wiktionary.org/wiki/gun#English

I think in this case the verb 'fly' is part of the expression 'will never fly'. It's a figurative way to say that someone or something will not succeed. Considering that 'talk smack' means to criticize someone/something, the individuals disrespecting and 'talking smack' about the person behind his back may try to convince the speaker that said person deserves the criticism and lack of respect he gets from them. However, they'll not succeed as the speaker doesn't seem to care and will likely remain on good terms with the person in your sentence, regardless of what anyone says about the latter.

It does, though I would personally use the preposition 'in' instead of 'during': 'I don't know what lies ahead in the next 9 years.' Another way to say/write the sentence: 'I don't know what the next 9 years hold for me/us.'

Despite the small difference, both sentences mean the same thing to me. However, I would rephrase them a bit: 'It doesn't help by coddling them. Rather, it does the exact opposite, and results in them being/becoming less independent.' 'It doesn't help by coddling them. Rather, it does the exact opposite, resulting in them being/becoming less independent.'

Hola Miguel ¿cómo estás? My name is Attila, and I am an advanced level English speaker looking for conversation partners with whom we could practice speaking. I would like to know if you are interested in having a conversation in English someday. If yes, then feel free to send me a message, we can talk about any topic you want.