Always a cool, hot guy, but never really a leading man, septuagenarian Sam Elliott is experiencing something of a renaissance.He has re-emerged as the sexy cinematic love interest of similar-vintage grand dames: Jane Fonda in “Grace and Frankie,” Lily Tomlin in “Grandma” and Blythe Danner in “I’ll See You in My Dreams.”Elliott’s iconic mustache has always been a veil of sorts, eliminating visual distractions from his sparkling, expressive eyes and the caressing rhythm of his …