Flavour, smack. The salt of youth is that vigour and strong passion which then predominates. Shakespeare uses the term on several occasions for strong amorous passion. Thus Iago refers to it as “hot as monkeys, salt as wolves in pride” (Othello, iii. 3). The Duke calls Angelo's base passion his “salt imagination,” because he supposed his victim to be Isabella, and not his betrothed wife whom the Duke forced him to marry. (Measure for Measure, v. 1.)
“Though we are justices, and doctors, and churchmen, Master Page, we have some salt of our youth in us.” —Merry Wives of Windsor, ii. 3.
“The Lord God of Israel gave the kingdom ... to David ... by a covenant of salt.” - 2 Chronicles xiii. 5.
“One does not eat a man's salt ... at these dinners. There is nothing sacred in ... London hospitality.” —Thackeray.
To sit above the salt - in a place of distinction. Formerly the family saler (salt cellar) was of massive silver, and placed in the middle of the table. Persons of distinction sat above the “saler” —i.e. between it and the head of the table; dependents and inferior guests sat below.
“We took him up above the salt and made much of him.” —
“M. Waddington owes his fortune and his consideration to his father's adopted country [France], and he is true to his salt.” —Newspaper paragraph, March 6, 1893.
A sailor, especially an old sailor; e.g. an old salt.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894