I'm not sure what the issue is. While yes, that is almost definitely fake, there has to be a cut off somewhere and it makes the most sense to put it where it's not likely to hit a real user but enough to catch legitimate mistakes.
Not a bug imo, the oldest living person is 114 years old, while I very much doubt they would actually frequent a forum, or even use a computer for that matter doesn't matter, still doesn't make it impossible.
I wonder if Bill Gates would still use a computer if he reaches that kind of age.
Maybe up the cut-off age to 125 or something? I mean, the oldest person ever was Jeanne Calment age 122 years. lol. You have 'atleast' 11 years then before it would need changing
It looks even more unprofessional if a user which is genuinely 109 and they're not able to show their actual age because of some power trick admin who doesn't believe in allowing the older generation to use their site as a youngster would.