If you mean as in "This here rifle has a hair trigger," it is substandard, but not wrong. Don't use it in writing.
The correct grammar is "You have been here for four months."
The correct form for this question is, "Did you leave your phone here?" If you are making a statement rather than asking a question, it is correct to say, "You left your phone here."
The correct grammar is "Here is some information." "Is" is used because "information" is an uncountable noun in this sentence.
Got here in 2 minutes before their cut off time is not a correct grammar.
No, it is not. It should read, "Did you leave your phone here?"
The sentence "I got here just 2 minutes before their cut off time" is correct grammar.
For more than 20 years of existence this may be my first time to visit here is not correct grammar.
For more than 20 years of existence i just now had the time to visit here is not a correct grammar.
Yes, the term 'here of late' is correct English grammar, as in: 'He was here of late, but he'll be in London next week.', which could equally be expressed: 'He was here [recently, lately, latterly], but he'll be in London next week.'
No, "will be had" is not a correct grammar. The correct grammar would be "will have."
"For so many years of existence i just now had the time to visit here" is not correct grammar "For many years of existence,I now have the time to visit here."
Neither one is really superior gramatically--they're just two different ways of saying the same thing.