Hi NeerajRajpal,
Since the overall 'content' of the GMAT has not changed much over the last several years, you would be fine using a slightly older version of the OG (such as the GMAT2018). That having been said, while the OG books are great sources for practice questions, they're not designed to teach you Tactics, patterns or the little 'secrets' behind the GMAT - for those, you'll need Course-oriented materials. To that end, you might want to consider working on the OG a little later on in your studies.
Before I can offer you any additional advice for your studies, it would help if you could provide a bit more information on how you've been studying and your goals:
Studies:
1) How long have you studied so far? How many hours do you typically study each week?
2) Have you taken any practice CATs/mocks yet? If you have, then on what dates (or approximate dates) did you take EACH of your CATs/mocks and how did you score on EACH (including the Quant and Verbal Scaled Scores for EACH)?
Goals:
3) What is your overall goal score?
4) When are you planning to apply to Business School and what Schools are you planning to apply to?
GMAT assassins aren't born, they're made,
Rich