Actually you are able to use the sketch feature on iPad 3s as well. What you need to do is:
1. Go into Notes
2. Select the back arrow
3. Select "On my iPad"
4. Create a new note
5. Type something random, anything. If you want, title the note.
6. Stop typing and touch somewhere on the screen that is not part of the new note you are typing. This will remove the keyboard.
7. When you view your new note without editing, you should see that there is a little scribble icon at the bottom of the screen. Select this.
8. You should now have the sketch screen open.
NOTE: This was only attempted after updating my iPad 3 to the latest update. This should work on iPad Air 2s as well. After the latest update, however, there is also an easier way on the iPad 3. It is as follows:
1. Open Notes
2. Start a new note; it doesn't matter what folder it's in
3. When the keyboard is open, you should see a little white line in the center at the very top, above all the letters. It's barely noticeable.
4. Carefully press and hold the white line and drag your finger/stylus towards the top of the screen
5. A new section of the keyboard should appear, and at the very right of this new section, you should see the scribble icon.
6. Select this to begin sketching.
NOTE: This new section will stick with the keyboard anytime you type, although the scribble icon will not remain. The section offers word recommendations as well as an undo and redo button, and the bold, italic, and underlined options. As a second note, you should be able to add a sketch to any note you've made in the past by selecting the scribble icon at the bottom right.