Native English speakers do say: I am liking this place already.

Yes it is quite ok. For example : I have done the cleaning already. John is in bed already. Enough already!

People do it all the time. It's OK. You can move English worder around to taste, to an extent, and even more so to give emphasis. A "straight" version might read "I have already known him for five years." But your version is very much in the modern idiom. https://learnenglish.britishcouncil.org/english-grammar-reference/still-and-no-longer-already-and-yet https://dictionary.cambridge.org/grammar/british-grammar/already https://dictionary.cambridge.org/grammar/british-grammar/adverbs-and-adverb-phrases-position https://dictionary.cambridge.org/grammar/british-grammar/word-order-structures https://books.google.com/ngrams/graph?smoothing=3&corpus=26&year_start=1800&content=for+five+years+already%2Calready+known+him+for&year_end=2019&direct_url=t1%3B%2Cfor%20five%20years%20already%3B%2Cc0%3B.t1%3B%2Calready%20known%20him%20for%3B%2Cc0#t1%3B%2Cfor%20five%20years%20already%3B%2Cc0%3B.t1%3B%2Calready%20known%20him%20for%3B%2Cc0

I don't know if it is grammatically correct. I'm sure someone else will know. It would be better to just say "I have known him for five years".