I doubt it's as high as 12 million people, but this is something I have seen in my work too. I wouldn't assume it's fraud. It could be in some cases, but it is more likely to be erroneous birthdates due to two-digit years. What I mean is if someone has a two-digit birthyear "00", they were probably born in 2000, but might be assumed to have been born in 1900 due to an old algorithm. 0000 or 9999 could also indicate a missing value.
https://www.ntd.com/database-lists-12-million-people-older-than-120-eligible-for-social-security-musk_1048177.html