Great job! That is awesome! I would start decreasing from 120 mg. But I wouldn't go down to 80 right away. I would drop one pill (10mg) a day for a while - at least a week. Make sure you still have an abundant supply. Then after a week or two, try dropping another.
I went down closer to 9 months and I think I did it too fast and my supply suffered a little.
Also, just wanted to let you know that typically a bf baby gains a lot less weight after 6 months and especially after 9 months, so he may drop on the curve, but that is normal. It doesn't mean your supply is not sufficient.
Jennifer