Question: In the South Park episode "You're Getting Old" which follows "Ass Burgers", Stan celebrates which birthday?

Context articles: South Park (season 15)
Rita Lakin
Big Gay Al's Big Gay Boat Ride
The Tale of Scrotie McBoogerballs
ManBearPig
You're Getting Old
Ass Burgers
Major Boobage
A Song of Ass and Fire
Douche and Turd

The fifteenth season of the American animated sitcom "South Park" began airing on Comedy Central on April 27, 2011 and ended on November 16, 2011.
 In response to reactions to the mid-season finale episode "You're Getting Old", which seemed to insinuate that creators Trey Parker and Matt Stone were wrapping up the series, Comedy Central proclaimed through the media that "South Park" was renewed for two more seasons, and the duo were signed through 2013.
 Shortly before the airing of the season finale episode "The Poor Kid", "South Park" was extended again until 2016, taking the show to 20 seasons.
 Parker was the director and writer for all episodes, and Robert Lopez was the writer in this eleventh episode for the fifteenth season.
Rita Lakin is an American screenwriter, with 474 produced television scripts spanning 30 productions.
 She is also a novelist and author of "The Only Woman In The Room," a memoire of her life as one of the first female show runners and one of the first women in television (released October 2015, Applause publishing).
 In fiction, Lakin created the Gladdy Gold Mystery seven-book series (published by Bantam Books), including "Getting Old Is Murder", "Getting Old Is The Best Revenge", and "Getting Old Can Kill You".
"Big Gay Al's Big Gay Boat Ride" is the fourth episode in the first season of the American animated television series "South Park".
 It originally aired on September 3, 1997 on Comedy Central in the United States.
 The episode was written by series co-founders Trey Parker and Matt Stone, and directed by Parker.
 In this episode, Stan's dog, Sparky, is revealed to be gay after humping a rival male dog.
 Under peer pressure, Stan tries to make him more masculine, and as a result, Sparky runs away and ends up at Big Gay Al's Big Gay Animal Sanctuary.
 Stan comes to understand homosexuality and tries to make everyone in South Park accept it.
"The Tale of Scrotie McBoogerballs" is the second episode of the fourteenth season of the American animated television series "South Park", and the 197th overall episode of the series.
 It originally aired on Comedy Central in the United States on March 24, 2010.
 In the episode, the South Park boys write a vulgar book with the sole intention of getting it banned.
 When Stan's parents discover the manuscript, the boys accuse Butters of writing it, then are enraged when it becomes hailed as a literary masterpiece.
"ManBearPig" is the sixth episode in the tenth season of the American animated television series "South Park".
 The 145th episode of the series overall, it first aired on Comedy Central in the United States on April 26, 2006.
 In the episode, Al Gore visits South Park to warn everyone about a creature called ManBearPig.
 On a trip to the Cave of the Winds, Gore ends up getting Stan, Kyle, Cartman, and Kenny trapped inside the caves.
"You're Getting Old" is the seventh episode and the mid-season finale of the fifteenth season of the American animated television series "South Park", and the 216th episode of the series overall.
 It first aired on Comedy Central in the United States on June 8, 2011.
 In the episode, Stan begins to develop a profound sense of cynicism after celebrating his tenth birthday, where he is literally seeing everything as "crap".
 Meanwhile, Randy latches onto a new music genre, "tween wave," in an attempt to fit in, which causes problems in his marriage with Sharon.
"Ass Burgers" is the eighth episode of "South Park"' s fifteenth season and the 217th episode of the series overall.
 It first aired in the U.S. on October 5, 2011, on Comedy Central.
 The episode picks up where the previous episode, "You're Getting Old", left off.
 Stan's cynicism is mistakenly blamed on his recent vaccinations and diagnosed as Asperger syndrome, a criticism of anti-vaccination proponents.
 Cartman mishears the condition as "ass burgers" and opens a food stand in which the secret ingredient involves stuffing his underwear with hamburgers.
 The episode is rated TV-MA-L in the United States.
"Major Boobage" is the third episode in season 12 of the American animated television series "South Park".
 The 170th episode of the series overall, it originally aired on Comedy Central in the United States on March 26, 2008.
 The episode was co-written by series creators Trey Parker and Matt Stone; it was the first South Park episode since 2000 not solely written by Parker, ending a streak of 120 consecutive straight solo episodes.
 The previous episode co-written by Stone was "The Tooth Fairy's Tats 2000".
"A Song of Ass and Fire" is the eighth episode in the seventeenth season of the American animated television series "South Park".
 The 245th episode of the series overall, it first aired on Comedy Central in the United States on November 20, 2013.
 The episode serves as a continuation of the previous episode, "Black Friday", in which the children of South Park, role-playing as characters from "Game of Thrones", are split into two factions over whether to collectively purchase bargain-priced Xbox One or PlayStation 4 video game consoles at an upcoming Black Friday sale at the local mall, where Randy Marsh has been made the Captain of mall security.
 The story arc concludes with the following episode, "Titties and Dragons".
"Douche and Turd" is the eighth episode of the eighth season of the animated television series "South Park", and the 119th episode overall.
 Written by series co-creator Trey Parker, it first aired on Comedy Central in the United States on October 27, 2004, just before the 2004 presidential election.
 In the episode, PETA forces South Park Elementary to change their school mascot, so an election is held to determine a new mascot.
 Stan ends up getting exiled from South Park after refusing to vote.