OK, thanks, I've learned something new, GNU Hurd has the edge over ReactOS by eight years. :-)

*Google*

https://en.wikipedia.org/wiki/Tandem_Computers: 1974 (50y) (semi-dead)

https://en.wikipedia.org/wiki/QNX: 1982 (42y)

https://en.wikipedia.org/wiki/VxWorks: 1987 (37y)

https://en.wikipedia.org/wiki/GNU_Hurd: 1990 (34y)

https://en.wikipedia.org/wiki/4690_Operating_System: 1993 (30y) (these run the self-service touchscreens at Costco's food section, IIUC)

It's surprisingly hard to query for "graph intersection between earliest first release date and most recent release date" :(

"gestation period" != age

I think the parent’s point was that Hurd is still unfinished. All of the others in your list shipped releases that met their intended goals in a much more compact timeframe.

edit: clarification

At least Hurd is making better progress than TempleOS these days.

I would say that TempleOS was complete considering Terry's goals.