Where does the term “old salt” originate

I know an old salt is an old sailor in maritime jargon, but where does the term originate. Does it have to do with the fact that sea water is salty? Why does the old salt have to be old, can’t s/he be just a salt (not assault, that’d be awful)? Or sea salt?

Apparently it refers to the salty water of the seas, according to Etymonline. Old refers to veteran, experienced:

Old salt:

Meaning "experienced sailor" is first attested 1840, in reference to the salinity of the sea.

Green’s Dictionary of Slang gives usage examples from 1830:

1830: N. Ames Mariner’s Sketches 7: The ceremony of shaving on crossing the line was omitted, to the manifest disappointment of the ‘old salts’.