I can't seem to find any option for switching Gmail from top-posting by default to bottom-posting by default. I can do it by manually expanding quoted stuff and moving the cursor, but I'd rather be able to have Gmail put the cursor where it needs to go without messing around with expanding and collapsing things. Plus, it would make things much easier when trying to explain to others how they need to format their emails for certain services so I don't have to handhold them anymore.
Click on the "1-50 of 1,234" text at the top right. It will transform into a drop down menu. Click and select the only option available.