Can I obtain dual citizenship and if so, what process do I follow?

A child born in France to foreign parents may acquire French citizenship:

At birth, if stateless.
At age 18, if resident in France with at least 5 years' residence since age 11.
At age 16 upon request by the child and if resident in France.
At age 13 upon request by the child's parents and if resident in France.
If born in France of parents born before independence in a colony/territory in the past under French sovereignty.
At birth, if born in France before January 1, 1994.
At age 18, if born in France on or after January 1, 1994.

So I guess I don't understand, if I have a French Birth Certificate and been in the US since I was 6 months of age, do I already have dual citizenship or should I apply for it and is it possible for me to obtain it?