Capitalization correction
Corrections 
Much more natural! (use more contractions > I'll, Can't, We're....
My comment
Plural

It's Gary!! haha!

Hi! How are you? I'm fine, and you? hahahahahahahahahahaha!!  (너무 많이 게리! ㅋㅋ)
Anyway, I'll tell you about myself.
My name is... Gary. But I'm not Gary :D
My real Korean name is Woo Kyuseok(or Kyusuk).
Don't be confused, Woo is a Korean last name! haha
I'm 23 years old. I wish I was younger.  (but I think you mean > 
                               I'm glad I'm not younger than  I am now.
Because my skin and body were not too good when I was 20 age.
My major is teaching for Korean language.
So I can teach korean to anyone.
But I should study english too.  (Yes!  I teach English to Koreans and I must study Korean too!)
Because I visited the United States (or the USA) to study English.
So, I lived in Georgia.  (past tense)
      I live in Georgia.  (present tense)
I had (have) two roommates. They were (are)very kind to me.
My hobbies are just talking, writing, and making friends and playing computer games.
When I was Korea, I spent time playing computer games.
But now, I don't play computer games. They don't have any meaning (to me).
I hope to make a lot of friends.
Making friends is so  really interesting.
So, if I continue to make friends,
I can make a good friend who will be with me forever.

Study ---->>>>>  Capitalization, Past tense of verbs, Plurals mostly. 
잘했어요!  네... REAL friends help REAL  friends. So we can be friends.  ^^

blue = capitalization and punctuation
pink = articles
orange = verbs
green = prepositions and conjunctions
red = nouns and pronouns
violet = adjectives and adverbs
light blue = my notes

It's Gary!! Hahahahahahahahahahahahahaaha!!!

Hi!  How are you? I'm fine, and you? (I didn't ask! ^^) Hahahahahahahahahahaha!!  Anyway, I will tell you about myself.  My name is... Gary.  But I'm not really Gary :D  My real Korean name is Woo Kyuseok (or Kyusuk).  Don't be confused; Woo is a Korean family name! Haha. 

I'm 23 years old. I wish I will be were younger than now. because my skin and body are too bad worse than when I was 20 age.

My major is teaching for Korean language education.  So I can teach Korean to anyone.
But I should study English. because I visited came in to the US to study English.

So, I live in Georgia.  I have two roommates.  They are very kind to me.  My hobbies are just talking, writing,and making friends, and playing computer games.  When I was korea, I spent a lot of time to playing computer games.  But now, I don't play them.  That don't have any means.  (Sorry, I don't understand this sentence.  Maybe you mean, "I don't have any way to play them."?)

I hope to make a lot of friends.  To Making friends is so interesting.  So, if I continue to make friends,
I can make have a good friends who will be with me forever.