Is there having any legal provision to keep our previous financial statements and verifiable objectives? if there is, how many years?

Law of limitation Act- require certain documents to preserved for a particular duration.

Evidence Act- same conditions.

Company Law and Taxes-no exception.

Our practice/ procedures /pending litigation (s)  all need be considered for a decision in this regard.

In many banks the vouchers and records are preserved for a minimum of10 years. In our company we used to preserve all records for a minimum of7 years. 

In cases of items which are seemingly  to important/and unresolved issues the records are kept for a permanent basis.

In case of Financial statements: it will always be helpful to keep the documents through the life period.  And for verifiable vouchers-maximum the period, the more on the safer side--but preferably a minimum period of7 years from the date of the completion of the transactions always be better.