Hello!
I'm using Age with Yubikey. Support for plugins was recently added to Age v1.1.0-rc.1 repository, but the validation still fails in SOPS.
Looks like the validation for identity fails because the parse-method of Age was never updated outside of Cmd...
Please look into adding support using Age with Yubikey, the plugin I'm using is this: https://github.com/str4d/age-plugin-yubikey

The commits inAge repo that adds plugin functionality : FiloSottile/age@cff70cf...87a982b

Example error:

sops --verbose --encrypt --age age1yubikeyreallylongstringherethatmakesupmypublickey file.yml
failed to parse input as Bech32-encoded age public key: malformed recipient "age1yubikeyreallylongstringherethatmakesupmypublickey": invalid type "age1yubikey"