I was wondering if the person is over 20 and the first language is not an English, do you think the person who can eliminate his first language accent to speak english like a native english speaker? I just wanted to know if it is possible?
It is possible. But you can't learn Finnish in Florida.
No, it's just a bit of fun because they both start with F. My meaning is that if you stay in Hong Kong, and use Cantonese for most of your everyday life, your English won't progress to the point it would if you moved to Alabama and lived without it.
It is possible but it is a lengthy process and requires full immersion in the language. It may take you years of practice in pronunciation and grammar.
It should also be noted that the ability to speak without a foreign accent does not guarantee you a native-level command of English - there are things that you'll have to master as well that are quite different in your native language and that naturally affect your perception of the world and the way you think of it. For instance, the notion of mass, countable and uncountable nouns of English presents a serious difficulty to some ESL learners because their native language simply does not have this feature.
Studies where native speakers judge the accents of (unseen) advanced non-native speakers (with all the proper scientific controls) show a low percentage of non-native speakers being judged as native.
So, it's possible but it generally doesn't happen - perhaps because by the time a NNS is fluent in grammar and vocabulary and their accent does not impair communication, there is no additional functional purpose in sounding more like a native speaker.
Here is a quote from Rod Ellis The Study of Second Language Acquisition OUP, 2008:
"Adult learners may be able to acquire a native accent with the assistance of instruction, but further research is needed to substantiate this claim" (p. 492).
I've lived in the US for 4 years now and I can tell that my spoken English has gotten much better compared to what it was when I came here (at that time, I had been learning it for about 15 years, so I didn't have much trouble adapting in the US.)
I can easily talk on matters related to my professional occupation and that is mainly because I'm familiar with the vocabulary, which is pretty static and quite limited.
Now, I still have some difficulty carrying on informal conversations on arbitrary topics, the so called "small talk". And the reason for that is that I often lack the necessary vocabulary. The difference between my cultural background and that of native English speakers also contributes to that.
The vocabulary problem can be relatively easily solved in a number of ways. Reading a lot is one of them - I read English fiction books and books on popular science, newspapers and magazines. Watching TV and listening to the radio also helps, provided that preference is given to talk shows rather than music programs.
As to the cultural differences, there is no other way to deal with them than by just accepting that they exist. I don't agree with the idea that one should abandon his own culture and accept the culture of the country he has come to. This may damage the person's nature, their feeling of self. There should be some kind of balance between accepting the new culture and keeping as much as possible of one's own.