Alex Gordon will be 32 years old next season, but he shouldn't have any trouble securing one final multi-year contract if (when) he declines his player option for 2016. From 2011-2014, Gordon was worth 22.4 fWAR, and in 2015, he posted a value of 2.8 in an injury shortened season.
According to Joel Sherman, Gordon might be able to secure a "four-year deal, perhaps even five years." As for the clubs that could be interested in his services, Sherman mentions the Astros and Cubs, and most surprisingly, the Boston Red Sox.
"Boston probably has too many outfielders for too few spots. But executives tell me that Red Sox officials have always liked Gordon and so has new Boston president Dave Dombrowski from his time in the AL Central as the Tigers' GM."
As of now, the Red Sox have Jackie Bradley Jr. penciled in for left field, Mookie Betts in center, and Rusney Castillo in right. If Boston is indeed serious about signing Gordon, one of those players would likely have to be traded, and Sherman notes that it could potentially be Bradley Jr.
"One scenario presented was that if Boston officials think Jackie Bradley Jr.'s strong finish inflated his value beyond his actual skill [set], this may be the best time to maximize dealing a young, defensive-star outfielder."
Bradley had an abysmal start to the season, as he posted a slash line of .133/.229/.233 with a wRC+ of 23 in his first 35 plate appearances; however once he began to play everyday, his statistics improved dramatically. From 7/29-10/4, Bradley accrued 220 PA's, and hit .267/.352/.539 with a wRC+ of 137.
Earlier this week, Jon Heyman noted that the Red Sox are "said to be more willing than in past years to trade top prospects to get the ace they need" and Bradley could undoubtedly be the centerpiece of a deal. He's just 25 years old, and is under team control through the 2019 season.
With Boston's need for pitching, it will be interesting to see who they might line up with during the offseason, but the Mets could make the most sense. They have a stellar rotation, but also a clear need for outfield help, as Yoenis Cespedes will become a free agent after the World Series. It remains to be seen how Boston will approach their offseason, but with a new regime in charge, they should be quite active between now and the start of spring training.