My son's father denied paternity for 40 years a recent paternity test prove positive
That he is my son's father. Can I file for child support from birth to 18 years old.

First, its not a good idea to put your question here./Children/

You asked a legal question.
No one can give you straight answer.It depends on so many circumstances-the state' law/it is forbidden a retroactive support order to be issued in some states/, and so on.