Every Indian Passport comes with validity of 10 years & Later it get expired, and its needs to be Renewed time to time making it valid, and Passport must be valid to travel.
The answer regarding your above query regarding passport renewal:
Its Highly recommended to apply for Renewal of Passport at least 1 year prior to your Passport expiry date, as in several countries likes Singapore etc for visa processing one should ensure that the passport has validity for 6 months from the date of entry in the visiting countries.
But its not like one cannot renew it if the passport is expired, One can still renew the passport, after it got expired no matter the duration.
One need to apply for Re-issue of Passport due to Validity Due to Expire or Validity Expired