If you're growing outdoors, the AF strain will take a little longer. It's not in a "controlled environment", so you can't tell it when it get's light, when it doesn't, etc...

If you're growing indoors, there's a few things it could be. Since it's an AF, it should have started flowering much more soon than 7 weeks (around week 3 or 4, maybe even earlier!).

Since your grow is going slower than normal, you'll need to look at the trichomes to determine when to harvest. Go to eBay and search for "Jewelers Loupe" and get a 30x magnifier! Then just watch those trich's til their good and cloudy, almost amber colored.

As far as why it seems to be behind on flowering, could you give me more information on your setup? I mean, it could be light leak during dark period, it could be too small of a pot (rootbound), etc. Anyways, I'm here to help...