I'm in the same boat with my first porter. It will be three weeks old this weekend.
I tried one last week, and it was tasty, but not to my taste. It was pretty sweet, and had a very caramel, toasted marshmallow, coffee with cream and sugar thing going on. I'm hoping the sweetness subsides with age.
What causes sweetness in beer? Is it unconsumed priming sugar? Complex sugars that yeasties can't devour? Some weird protein effect? The recipe itself (the "Ultimate Porter" from BYO) didn't have anything weird in it (just malted grains, extract, and hops), so the mystery sweetness has piqued my curiosity.