Where does “Gerontius” come from?

Gerontius (Latin) comes from Ancient Greek γέρων, from Proto-Hellenic *géronts.

Ancestry of “Gerontius”, step by step

Step	Language	Word	Meaning
1	Ancient Greek	γέρων	an old man; elders, i.e. a ruling or advisory...
2	Proto-Hellenic	*géronts	—