> least fifteen years
That's actually expected since the distro itself is quite new. It was created to allow SteamOS 3.0 "Holo"* to be installed outside Steam Deck, so it can't be older than the machine.
*Contrary to previous versions, you can't install 3.0 on any machine. You can still download "image", but it's only usable on Deck and to my knowledge it's also stripped from every driver it doesn't need (even HoloISO doesn't support Nvidia cards).