What specifically is the dividing line of a generation? Most people use cultural moments in history. If you can remember Pearl Harbor, JFK getting shot, the Landing of the Moon, before the Internet, etc... as dividing lines to a generation.
It is very liquid and non-specific kind of marker and not always fixed. Thus anyone born before the 1980s can remember growing up before the Internet. People born in between 1984 and 1894 are all a part of the B.T.I generation - Before the Internet.
Some people use the average length of childhood to mark a generation. Basically if another person was not able to have been your father or mother; and you were not able to have been their mother or father; then that person is a part of your generation.
With that biological definition of generation, a person born approximately 12 years older or younger is a part of your 'Biological Generation.'
If you were born in between 1948 to 1973 then you are a part of Barack Obama's Biological Generation
If you were born in between 1918 to 1943 then you are a part of Will Shatner's Biological Generation
If you were born in between 1982 to 2007 then you are a part of Justin Beiber's Biological Generation
If you were born in between 1938 to 1952 then you are a part of John Lennin's Biological Generation
....whichever generation you fit into, that means that man could not have been your father, nor could you have been their father or mother.