Throw in the insane amount of money Joey owed Chandler by the end of the series’ run, and I think it’s safe to say that old Joe just wasn’t great when it came to numbers… or accents.
Obviously, the joke is funny on its own, as Joey can’t remember how old he was at a certain point in 1990.
Hilariously, this wasn’t even the only time that Chandler would be called upon to point out Joey’s age confusion.
Matt LeBlanc wasn’t exactly over the hill and aged in 1995, but he was clearly more than 20 or 21.