I found out (in my 30s - I'm now 50) that neither of my grandfathers was my biological grandfather.
I know the names of both of my biological grandfathers, but I've never been interested in knowing anything about them or their families.
Part of me would like to know more about health histories, but not enough for me to pursue.
The biggest impact this has had on me that I'm actually aware of is that I grew up telling people that I'm Puerto Rican and Italian .... and now I know that the only Italian thing about me is my last name. This, after giving my son his middle name after my great grandfather's first name (Vincenzo), only to find out that I have no blood relation to him and, obviously, nor does my son.