Marrying with an age gap of 20 years or more.....

Hello! I can't marry a person who is 20years or more years younger than me because there is no such boy. I am just 19yrs old. So now if I had to marry a person 20 years or more older than me, I would never marry because he would look like my uncle, not husband. So I think am never going to face such situation of marrying with an age gap of 20yrs or more. And I believe that in a marriage the age difference should be maximum 6 years. I mean the age difference should be 6yrs or less. I have heard about some people who have married with a person who is of their son/daughter's age. Also I have heard about people marrying somebody who is their grandchildren age group. They say they fell in love, etc. But I really don't understand how this happens. I mean this speaks LOVE is BLIND.