This has surely got to be "It’s A Bunch of Years After The War And Everything Is Different", a humorous piece by Daniel Mallory Ortberg dated 11 February 2014. It's short but here are a few choice excerpts, emphasis added by me:
It’s a bunch of years after the war. It has been exactly seventy-seven years since the war. It’s been two generations now, since the war. It’s like a mabrillion years after The War. Ohhh my Godddd, it’s so many years after the war.
Today’s the day the thing happens. The one big thing that happens to you nowadays — only one Thing happens to you, and it happens to everyone. Today’s the day of the test. Today’s the day of the Sorting. Today’s the day we are Chosen. Today’s the day we go to the City and get selected. Today’s the Thing Day. Normally one thing happens, but this time a different thing will happen, because of how different we are, which is unusual. There’s only five things you can be, but I’m a different thing. Society just made everyone pick one thing, somehow. You have to wear the matching jumpsuits or else you’re the wrong thing.
You’re so different. You’re so strong. You’re so brave. You don’t know how brave you are, which is what makes you so brave. You’re not like all of the others. You’re different, the way that you are. Not like the way things normally are. Which is bad, because here in the future, everything’s the same except for you and your sensible ponytail.
I told him I can’t trust anyone, and he said Okay but you can trust me so I did so now I guess I trust one person and it’s him. How can I be different? I’m not different. That’s what makes you the most different of all, he said. I don’t trust anyone either, he said, but let’s take our shirts off in this abandoned old building that probably used to be a warehouse and then trust each other.
I think I stumbled across this by a lucky chance. After several different tries with Google using different search terms, the winning query was
parody dystopia "years since" "trust me" - which gave this page as the first hit even though the word "parody" doesn't appear.