"if he was" and "if he were" ... to be or not to be. That is a question.
what is the difference between "if he was" and "if he were". Is it possible to use the 3d person form past in the conditional sentences?
I know it is possible to say something like: If I were you, I would meet her next day.
or "If Mike were here, he would kick your bum".
or "She treats him as if he were her son."
or "If I were a millionaire I would spend all the money for charity.

However, as far as I know it is not okay to use If he was..... and bla bla... What would you, guys, say?

Question

"if  he  was"  and  "if  he  were" ... to  be  or  not  to be.  That is  a  question.
what  is  the  difference  between  "if  he  was"  and  "if  he  were".  Is  it  possible  to  use  the  3d person form past  in  the  conditional  sentences?  
I  know  it  is  possible  to  say  something  like:  If  I were  you,  I  would  meet her next day. 
or  "If  Mike  were  here,  he  would  kick  your  bum".
or  "She  treats  him  as  if he were her  son."
or  "If  I  were  a  millionaire I  would spend  all the money  for charity.

However,  as  far  as  I  know  it  is  not  okay  to  use If  he  was.....  and  bla  bla...  What would  you, guys,  say?

Answer

At one time the correct use of the subjunctive was only "If I were..." however, this expression is becoming somewhat colloquial. These days, you will hear many native English speakers say, "If I was...".   Both expressions are considered correct (according to most sources), however "If I were..." still seems to hold more of an "educated" reputation.

Answer

If you want to talk about imagined (or unreal) situations in the present, then "were" is the correct form of the verb.

However, it's becoming common to use the simple past "was". Even though it's not traditionally correct, it still fits the rule of using the past form of the verb in 2nd conditional (=imagined present) sentences.

I still use "if I were...", "if it were..." and so on. That rule is still valid.  "If I was you, I'd...." still sounds like a mistake, though.