1. If the VISA officer asks why should I grant you VISA what should I answer?

my only purpose of trip is to get good education and global exposure.To achieve my goals in life you must grant visa

2. Is it possible in "any" way to get a visa to work there, (and has the skill for a field) if the age of the applicant is over 45?

I think it is posible to get the sub class 457 work
visa ,because age is not the criteria for the same.it
requires sponsorship from the australian employer based on
ur skill
457 is used by most of the indian IT Consultantts.
..for more info visit immi.gov.au

3. I have following bands in IELTS (Speaking: 7.5, listening:6.5,Reading:6.5, writing:5.5)... Overall Band Score is 6.5/9.0. Am I eligible to apply PR for Australia?

it depands upon many thing wlike your
qualification,experience,chk australian immigration
website,thats very helpful
http://www.immi.gov.au/

4. How much time it will take Get Australia Visa?

first check the DL(Demand List)/SL(skilled list) in the immigration website, don't trust any consultant. in general PR process might take 6months to one year. if you are lucky it might come within a month also.

5. What is the difference between the expression a4 and a[4]?

it is very simple answer according to the way you asked the
question what i mean.

just see very close to the both 4s with the expression

The answer is

1) the digit 4 in not in the braket campare to other one.

2) the digit 4 is in the braket.

6. How you spend your yesterday?

Hi, First of all do not get tensed. Just keep yourself cool
and clam. The most important to the Visa Interview is "never
fake" or "never lie" just represent who you are and what you
are. Secondly always your answerer should be sweet and
short. Well in such situation just say O ya my yesterday was
too good, was with friends whole day as they came home to
wish me all the best. Finnish your ans quickly without
waisting any time and with full confidence.

7. I would like to apply for PR under Skilled Migration Visa for Australia am I eligible or not?

First of all you need to write a Competency Demostration
Report(CDR) for assesment of your qualification by
Institute of Engineers Australia.
After Sucessful completion of assesmebt you will be
ellegible to apply for immigration or permanent residence.