Here is all the info, ordered by release date:
Device Launch Version Final Version Lifespan
Nexus One 2.1 Eclair 2.3 Gingerbread 1y 1m
Nexus S 2.3.6 Gingerbread 4.1.2 Jelly Bean 0y 8m
Galaxy Nexus 4.0.4 Ice Cream Sandwich 4.3 Jelly Bean 1y 7m
Nexus 4 4.2.2 Jelly Bean 5.1.1 Lollipop 2y 6m
Nexus 7 (2012) 4.1.2 Jelly Bean 5.1.1 Lollipop 2y 8m
Nexus 10 4.2.2 Jelly Bean 5.1.1 Lollipop 2y 4m
Nexus 7 (2013) 4.3 Jelly Bean current* N/A: Launched 2013-07
Nexus 5 4.4 Kit Kat current* N/A: Launched 2013-10
Nexus 6 5.0 Lollipop current* N/A: Launched 2014-11
Nexus 9 5.0 Lollipop current* N/A: Launched 2014-11
Nexus Player 5.0 Lollipop current* N/A: Launched 2014-11
Nexus 5X 6.0.0 Marshmallow current* N/A: Launched 2015-09
Nexus 6P 6.0.0 Marshmallow current* N/A: Launched 2015-09
Pixel C 6.0.1 Marshmallow current* N/A: Launched 2015-12
*current version is 6.0.1 Marshmallow
So starting with the Nexus 4, devices have averaged 2.5 years between their release and final update. You should add on a few months to account for the fact that there was some time between their final updates and when that version was actually obsoleted by the next. And the 5 and 7(2013) have passed that mark, though they will probably not get Android N.
Sources: