Some teachers say that maybebelieve that, while not everybodyone can't learn a language through reading and writing but everybody, most can definitely learn through listening and speaking.

1) Breaking up this sentence with commas like I have done in the revision improves its readability.
2) While ‘everyone’ and ‘everybody’ are both singular indefinite pronouns that can be used to mean ‘all of the people (in a group or in general)’ or ‘every person’, ‘everyone’ would better suit the more formal tone of the rest of the paragraph.

They argue that every normal kidse teachers would argue that most children can learn their mother tongue naturallin such a way.

1) Because two separate entities are defined in the previous sentence (language teachers who hold this belief and all people learning foreign languages), it would be best to clarify who ‘they’ refers to in this sentence.
2) While both terms mean the same thing, ‘kid’ is a colloquial term, while ‘child’ is a formal term. Considering the more formal nature of the paragraph, ‘child’ would be a better choice.
I suggest removing the ‘normal’ adjective preceding ‘child’ because ‘normal child’ can carry some negative connotations that may distract some readers from your argument.
3) Rephrasing what you mean by ‘naturally’ adds clarity to the sentence and connects it with the previous one.

Whether you are young enoughIn foreign language learning, one’s age and whether youthey have access to a language environment are very important.

1) Adding a transitional phrase such as the one I’m suggesting in the revision connects this sentence with the previous one and improves the flow of the paragraph.
2) While one can use ‘you’ to refer to people in general, it is also important to remember that ‘you’ is also a second person pronoun that is commonly used to address another person or group of people in writing or conversation. In this case, it is difficult to determine whether ‘you’ refers to people in general or if it is intended to be a direct address to the reader. This can confuse the reader and potentially detract from the effectiveness of your argument. As such, I would argue that it’s better to use ‘one’ rather than ‘you’, as ‘one’ can be used to refer to people in general without potentially being interpreted as a second person pronoun.
2) It would be more efficient to say ‘age’ rather than ‘young enough’. The latter can also be interpreted negatively (like, in an ageist manner) and turn readers off from your argument.
3) It would make more sense to say ‘have access to’ rather than simple ‘have’.

Otherwise you can hardly pick upWithout taking either into account, one will experience difficulty in learning the foreign language easily.

1) Replacing otherwise with a transition similar to the one suggested in the revision improves the sentence’s clarity.
2) The ‘easily’ you included at the end of this sentence is a bit redundant, as you already established that there is an element of difficulty with the inclusion of ‘hardly’ earlier in the sentence.
3) See the first point of my feedback for the previous sentence for why I use ‘one’ instead of ‘you’ here.
4) It would be better to use ‘will experience difficulty’ rather than ‘hardly’, because ‘difficulty’ is a noun that states that something is hard to do or accomplish, while ‘hardly’ is an adverb that means ‘almost not’ or ‘barely’.
5) ‘Learn’ would work better than ‘pick up’ as the latter is more abstract than the former and may serve to confuse the reader which can detract from the efficacy of the argument.

I have many students who are havexperiencing difficulties in learning English.

‘Experiencing’ is a better choice of word than ‘having’ because the former indicates that something can be gone through/experienced while the latter typically indicates that something is a possession or can be possessed.

Their one-on-one tutors said that theyhave told me that these students forgot what they had learned faster than they learned something new.

1) In the original sentence, it is unclear who the one-on-one tutors are directing what they have said to. Replacing ‘said’ with ‘have told me’ (or, alternatively, ‘have told these students’) clarifies this.
2) It is unclear if the first ‘they’ included in this sentence refers to the tutors or the students. Replacing it with an explicit reference adds clarity to the sentence.

Some teachers say that maybenot everybodyone can't learn how to reading and writinge, but everybodyone can definitely learn how to listening and speaking.

Whether you are young enough and whether you have a good language environment are very important.

Otherwise you can hardlynot pick up thea foreign language easily.

I have many students who are having difficultiesstruggling to learning English.

'Having difficulties' makes sense, but I think it's more natural to say something like 'struggling to'.

Their one-on-one tutors saidy that they forgoet what they had learned faster than they learned something new.