This is one of my finding in Facebook which i want to share with you all.
While searching for bugs on Facebook, i came to know that you cant post anything beyond your birth date. ie if your birth date is 01/01/1970, you cant publish a post on 31/12/1969. So i started playing with this.
suddenly i realised ,if i cant post anything beyond my birth date, that means even my friends wont be able to post beyond their birth date as well. So i created one post and tagged my friend and set date to something around 1970(example) and published a post. I checked my friends timeline and no year appeared on the right side of the timeline( you see year queries on timeline on right side). so i again edited the same post and changed the year to 1971. again it did not appear on timeline. I did this several times (decrementing the year one by one ) and suddenly the year appeared on timeline.
After testing for a while, I realised, the year which is printed on timeline is 1 year less than birth year of my friend. i.e if your friend birth year is 1989, you will see 1990 year printed on timeline. you wont see 1989.
This should work for friends who are younger than you as you cant post beyond your own birth date. if you want to find out the birth year of elder friends, you can just adjust your birth year for time being to something greater.
Reported this to Facebook but unfortunately i got the following response