sounds like you are doing a great job and the key thing I read was that you are demand feeding, he is demanding it. My DS was a very frequent feeder and would feed every 2/3 hrs even at 8 mnths but that was probably more snacking then feeding cause he would literally be done in 2 mins. At your DS age he is now a pro and very efficient so it is not surprising he isn't taking that long to feed now.