> trusts this specless tool will be maintained forever

As per the third sentence of the readme there indeed is a spec[0]. There is also an alternative implementation in the form of rage[1], as well as numerous others listed on the awesome-age page[2].

[0]: https://github.com/C2SP/C2SP/blob/main/age.md

[1]: https://github.com/str4d/rage

[2]: https://github.com/FiloSottile/awesome-age