This can be achieved via changing the system clock. Simply set your system clock to the last day of a previous month, and you will have access to all of the challenges and medals for that month, so you do not need to spend an entire year pursuing these achievements.
To illustrate, pretend this had been posted in January 2018. I would set my clock to 12/31/17, and do challenges until I have received the December 2017 gold medal. I would then set the clock to 11/30/17, and achieve the November 2017 gold medal. I would do this for each month until I have achieved all of the gold medals from May 2017 through December 2017 to give me "Go For The Gold." Since I would have also achieved the silvers and bronzes for these months on the way to the golds, I would then just need to achieve the silver medals from March and April 2017 to give me "Go For The Silver," and finally achieve the bronze medals from January and February 2017 to finish up "Go For The Bronze."
Note that the specific months used for this don't matter. You can get your medals in any order from any year since the game has been released. The example used was chosen for simplicity.