User blog comment:RRabbit42/Birth and death dates/@comment-961279-20111010054141

These and Simpsons World (for Seasons 1-20) appear to be the only books that have been written by Matt Groening about the show. So far, I am not seeing anything that lists specific years for the characters. In fact, the Simpsons Family Tree inside the front cover of The Simpsons Family Album is the only place that a lot of the characters are mentioned and it's just a picture showing who's related to whom. A random sampling shows that adding these dates only started this year and there's just a few accounts and IP addresses doing it.

Based on this, I have to conclude that any birth year, death year and age on these pages is false information. Whether it's deliberate vandalism or just people who think they need to fill in biographical details, it can be removed as unsourced fan fiction.