I think you should post this kind of comment on "Answers" not on "Discussion".

But anyway I would answer your question.

1. to male friends of same age. →　僕　or  俺
2. to female friends of same age.　 →　僕　or 俺
3. to senpais. both male and female.　→僕　or  私
4. to teachers and other formal relations.　→私

As you know, using 俺 is rude.  So you should use it only for your close friends.

We Japanese seldom use あなた.

We call someone by their name adding さん or くん or ちゃん.

さん is for anyone, くん is for young boys, ちゃん is for kids.

If the person we are talking to is a teacher, a doctor, a lawyer, a politician or something like that,

we call him/her 先生.

If the person we are talking to is our customer, we call him/her お客さん or お客様(more polite)

If you talk to someone you don't know his/her name, you can call him/her

おにいさん（for young guys 20's ~ 30's or 40's)

おねえさん（for young ladies 20's ~ 100's)    Women in any ages like to be called "おねえさん”

おじさん（for men older than around 50’s)

Although there is a word おばさん for women in their around 50's ~ 60's, never call them おばさん.

You will be killed.　;P

Ah! so that is why no one commented. I had just made the italki account si I didn't know. sorry.


Oh I see. In my country though, if you use the equivalent of 'obachaan/obaasan'  to quite old women, it would mean instant affection. But, I see.

That is just scary, sisterzoning a whole country.
I kid, I kid. Sorry for the weird western joke.