The IPv6 standard (RFC 2460) was finalized in December 1998. IANA and the first RIR ran out of IPv4 addresses in first half of 2011. During the decade between those two events the Internet should have been upgraded from IPv4 to dual stack such that new hosts after that point could be made IPv6 only.

At the start of 1999 a typical network would be IPv4 only, and by the start of 2011 it should have been all dual stack. Assuming 1% of hosts upgraded in the first and last year, and a logistic growth between those, you get the table below. It has been extended beyond 2011 assuming transition from dual stack to IPv6 only would take the same number of years.

This is not an official transitioning plan. It is just meant as a reference for you to figure out roughly how far behind schedule you are in upgrading your own network. The Internet as a whole was at 1% dual stack at the start of 2013 according to measurements by Google, putting the transition 13 years behind schedule.