No. You can only do so post-facto in the shape item's properties. Other than that you can always create an animation preset.
Draw your shape with the Ellipse tool then select the shape layer and press the U key twice to reveal the shape layer properties. Manually type in the size of the eclipse and then reset the Position property of Ellipse 1. That will take you from this:
And give you a circle, perfectly centre on the anchor point of a specific size that you can then animate.
The other option would be to use a solid with a mask for your ball. Simply create a 200 X 200 solid then select the Elipse tool and the Solid layer, making sure the tool is set to mask and double click the Ellipse tool.
If you are creating tutorials about using shapes and you want to be taken seriously you should first type Shape Layers in the Search Help field at the top right corner of AE and follow the links to read up. About 90% of the YouTube tutorials on After Effects demonstrate inefficient and ineffective workflows and at about half of them teach techniques that develop very bad habits. Please study up.
gives you this:
Thank you for your enthusiasm. I'm well aware of Adobe's help Bible but I'm trying to figure out the simplest way(s) to use AE for first-time-users, limiting the number of steps before getting results, so creating solids it's out of the question, and so on. It's curious that after all this time there's no simplest way to input the sizes before drawing the shape, nevertheless, the quickest way (brought to my attention by Johnny Cuevas), would be to use Layer > New > Shape Layer to add the layer to the project. Then in the contents "ADD" flyout choose ellipse, and enter in a size. Next use the "Add" flyout to give your elipse a fill, so there's no need to reset the anchor point.
If you are doing a bouncing ball you probably want to set the position property of the circle so the anchor point moves to the bottom. Just a thought. I find my method a little faster but to each his own.