Can I buy a nifty option contract for a period of six years?

No, You not able to Buy Nifty Options Contract for 6 years because Options Expiry Monthly weekly.

and Yearly but not Volatility in Yearly and Second Month Contract so You Not able to Buy Nifty Options for a Long Period.

So I suggest you please Avoid for Long Term in Nifty Options Only Buy for Short Maximum One Month. After Month Square off Your Position and then Re-Buy in Next Month Contact.