Are you claiming that the Sequoia implementation of the OpenPGP standard is a "complicated old mess"? Because the OpenPGP standard (RFC 4880) isn't really all that complicated. A significant portion of is a bit by bit description of the key format.

At any rate, age is hardly any sort of replacement for OpenPGP. It is really only suitable for the case where you want to encrypt something like a backup and not bother to sign it. I am not really sure that it is superior even for that niche case. Most people would want to know a backup is corrupt before they started the restore, not partway through it.