I remember my Birthday because it's usually Martin Luther King day, my brother's is 10 days after St. Patrick's day, my dad's is on the 4th of July (if you ever met him, you would probably find this as some sort of irony.), my mom takes a bit to remember sometimes but it's June 24th.
However I'm ashamed to admit that I forget my mom and dad's ages pretty much all the time, it's probably because my mom is in her early to mid 50's and my dad is 9 years older.