Our 4spd T Line is 18lbs 4oz ready to ride. A C Line ebike w/battery mounted is 39lbs 6oz. A standard C Line 6spd is 26lbs 7 oz. I once put a BSO folding ebike with front suspension and mag wheels on a Park Tool scale and it wouldn't weigh it,max weight was 55lbs.

Average weight really isn't a thing given how many different folding bikes there are. There are bikes with wheels from 12" to 700c,steel/aluminum/carbon,derailleur and IGH bikes. A better question would be to ask what kind of folder you're looking at generally weighs.