Want to feel old? The 'want to feel old?' factoid meme dates back to around 2011, closer to the Bush/Kerry election than to today.
Cueball tells Megan that by the release of this comic in April 2018 it is the 10th anniversary of the peak of rickrolling. Rickrolling is a bait and switch internet prank, in which a person is tricked into clicking on a link under some pretext, and is diverted to a music video of Rick Astley performing his 1987 hit "Never Gonna Give You Up". This trend began in 2007, but reached a peak in about April 2008 when, as an April Fools' Day prank, Youtube linked all its featured videos to Never Gonna Give You Up. At nearly the same time, the New York Mets held a public vote to choose their 8th inning sing-along, and fans organized to vote for "Never Gonna Give You Up". This coincided with a sharp peak in searches for "Rick Astley" and related terms.
When Cueball points out how long ago this happened, Megan expresses surprise that the phenomenon was that old, then expresses a half-hearted happy anniversary wish. After a beat panel Cueball concludes "We've known each other for so long", which is both a poetic affirmation of his friendship with Megan, and a line from the song, which effectively turns this conversation into its own version of rickrolling.
The first reference to rickrolling in xkcd was in 351: Trolling from 2007, where Astley himself was Rickrolled by Black Hat. Black Hat then later uses Astley to show his girlfriend Danish how Rick rolls in 524: Party, a New Year party from the end of 2008.
The title text refers to another old xkcd meme of giving snippets of information to the reader that make them feel old. Although comics such as 218: Nintendo Surgeon in 2007 refer to facts that could make you feel old, the first comic directly build around factoids to make one feel old in xkcd was 891: Movie Ages in April 2011. This was 7 years before the time of publishing. The Bush Kerry election was in November 2004, 6½ years before that comic, making the title text statement that the beginning of this meme is closer to that election that today. This is the way most of these make you feel old comics are built.