A Bike Frame Question?

The frame of any bike is only about 15% of the total weight of the bike. So a frame that is a bit heavier isn't going to make a huge difference in the total weight of the bike. However, a 20" frame is going to be quite big for you. Sure, you can lower the saddle, but the top tube is going to be high, and probably too long. Fit is going to be a much bigger issue than weight