"Leathery" is a winespeak term used to describe wines—typically red wines—that are very high in tannin. Tannin, you may or may not know, is the same ingredient used to tan leather, preserving the rawhide in much the same way that it allows wine to age slowly. You probably wouldn't drink grape juice left in the pantry for 20 years, but what about a bottle of 1975 Lafite-Rothschild? Sure, because the latter has been stabilized and preserved via its tannin and alcohol.