How many Mainland Chinese can learn English to the level that we can? A very small percentage. They are using Mandarin all the time, they will lose their English. I will give you an example. I used to meet the Taiwanese ministers, the older generation - all Harvard PhDs. In other words, they wrote their theses in English but worked in Taiwan in Mandarin. When I went to Taiwan, I spoke to them in Mandarin, first two days (my Mandarin was) very stiff. At the end of the week, I was more fluent. They came here to meet people from our ministries, first two days their English was halting, at the end of the week they became more fluent.
Learn young, never mind the standard, capture the fluency, capture the way you speak it, capture the grammar, never mind if your vocabulary is limited, you can expand it later on.
You need to spend the time and effort. You must have the interest. At the end of the day, it must be a live language. Apart from watching it on the TV or reading the newspapers, you must meet people and talk. Then it is a live language.
Language is heard and spoken long before people learn to write and to read. The more frequently one uses a language, the easier it is to express one's thoughts in it. The younger one learns to speak a langugae, the more permanently it is remembered.
I may speak the English language better than I speak the Chinese language because I learnt English early in life. But I'll never be an Englishman in a thousand generations and I have not got the Western value system inside me; it's an Eastern value system with the western value system superimposed.