When a 10-year-old registers for an adult website, they pretend they're 100 years old. Their age is 90 years different from the stated birthday. Eighty years later, the birth date is just as far off—but the implied age is now only 10 years off.
Thanks this seems like the correct meaning rather than the other comment. But that is beautiful its own way, got me all philosophical.
We're keeping the same date here. 80 years later, the site thinks they're 180 years old. So it's still 90 years off, but now it's only 2x off instead of 10x off.