You need to create two forums for each forum to do this.
1. The welcome forum should be shown to Users, and hidden to the rest.
2. The real forum should have access only to the group to be allowed in. No access to 'Users'.
What you then need to do is take every member of each group and remove them from the "User" group.
You then have to adjust all forums to treat the Male and Female groups with the same access rights as a 'User'.
Then a male user will only be a Male member. They will have access to all forums that a "User" had before, but blocked from forums that "Users" have access to and "Male"s don't, because they are no longer a 'User'. Males will see forum #2, but not forum #1, Users will see forum #1 but not #2.
Hope that helps.
Here's another thread that is like this:
Blocking user groups