Haha I had this exact experience, we showed up for a Halo lan party (the original) and we were 15 and 16 thinking that we'd be driving out to the burbs to play some games with some people our age, we met on a local LAN forum board.
We rang the doorbell and an "older" man answered the door, and we were confused and said "uh we're here to see ____" and he was like "That's me."
For context all of our lan parties up to this point were us schlepping tube tvs around to various basements of our friends houses, occasionally getting to mooch some pizza off of someone.
Instead, we walk into the huge suburban house and there's four rooms with gigantic flat screen televisions setup for 16 player madness and the entire place is filled with adult couples, the men came to game and the women to socialize and cook and have fun.
They had an entire table of snacks and drinks and everything you could ever want as a wee gamer.
We were so blown away but they were super nice and didn't make us feel too awkward. When the game started they asked us how good we were, "uhh, we beat legendary" - they laughed and put us on the same team for the first round.
The second round we were not allowed to play on the same team, turns out the kids can game :)
We made long term friends and ended up scrimming and hanging out with people 20 and 30 years our senior, a total blast and yeah, I don't see me hanging out with 16 years today.