Four years isn't a significant period of time. A handful of college students don't finish a college tenure in that time. The President of the United State does, but only in that exact amount of time.
But, in football years, four years is seemingly an eternity. The Texans and the Vikings are a few of the rare teams that actually have players that have stretched that time frame. There are teams throughout the league that only have a single non-specialist from 2012 or earlier on their roster and some that don't have one at all. The NFL has seemingly become younger and younger by the year and there's fresh blood on every team in the league. It's not sustainable without it.
However, the Vikings will start as many as four players on the offensive side of the ball that last played against the Texans in 2012. Throw in Matt Kalil and Adrian Peterson, both of whom got hurt early in the season, and, at the outset of the 2016 season, the Vikings returned over half of the 2012 starting lineup that came to Houston and beat the Texans in 2012.
In contrast, the Texans only have two players on that side of the ball returning from 2012 - Derek Newton and Duane Brown. Still, that's one or even two more than a good majority of teams in the NFL have.
The Vikings defense only has three players from that 2012 team, but they're all-stars on that unit. Chad Greenway, Everson Griffen and Harrison Smith have been mainstays on the Vikings defensive unit over the past five seasons. The Texans have four players from that 2012 game, not including Brian Cushing who was injured during that AFC South championship campaign.
In total, there are about a dozen players that were part of those 2012 rosters the last time these two teams played one another. Look around the league. There aren't many players that have been with teams in that four year time frame. The Vikings and Texans don't have many, but they combine to have as many in this game as any two teams will have in any matchup in the NFL this weekend.