The old kernel in grub2 is in a submenu entry in a menu. The key is to set the submenu as the default entry for grub2.
To select a submenu in a menu, e.g. “Fedora, with Linux 3.8.3-103.fc17.x86_64″ under “Advanced options for Fedora”:
# grub2-set-default ‘Advanced options for Fedora>Fedora, with Linux 3.8.3-103.fc17.x86_64′
Note the ‘>’.
For the other steps, just follow this tutorial: https://www.systutorials.com/b/linux/3826/setting-default-entry-in-grub2-and-grub/