Short loin anyone?

You can certainly dry age a 7-bone bone-in ribeye, but I’m not sure you’ll ever get a 21 pounder into the Short Loin size (16 x 28 in) UMAi Dry® bag.
Make sure you cushion the ridge of bones with kitchen parchment to prevent punctures, and expect it to be hard to get good overall contact. The only meat exposed is on the ends. The rest if fat cap and bone shell.
Check out this video for some great pointers:

Maureen
UMAi Dry® Customer Support