Technically Lifespan is a stat every unit has access to as long as Babylon is enabled. Heroes are the only Firaxis-made units which have a set Lifespan. Some mods may add new units with a Lifespan, such as my Nepal, or rework existing units to expire after a while. I gave base game Juba use it to make him stand out as the premier leader of antiquated medicine.

Cool! Is the +15% Lifespan mainly for Heroes, or is there some other application that I'm forgetting?

Which Barbary civ is next I wonder?