Yesterday I brought home a new male gsp who is 4.5 months old, and I already have a 1 year old female who is very submissive, but gets very excited to play with other dogs.  I got our new male from the same breeder that our female came from a year ago.  He seemed very socialized at the breeder; playing with other dogs and showing no aggression whatsoever.  When I brought him home he would show aggression by growling and pouncing on my 1 year old female, who immediately submits.  This seemed to happen everytime my female would be excited around him and try to play. 

Is this behavior typical?  Could it maybe be because he was stressed in a new environment and was also scared?  I'm guessing that he is trying to be the dominant dog in the pack, should I just let them work it out, or should I step in as the alpha in the family and not allow the agression?  Any advice would be greatly appreciated, thank you!

 I agree with TB and PB, he's still a pup, but I wouldn't let it continue if TB's advice doesn't work (although I think it will, it's just a matter of them getting to know each other).