The initial idioms of the letter O

old man	old money
Old Nick	old one-two
old poacher makes the best gamekeeper	old saw
old school	old school tie
shadow of one's self	old sins cast long shadows
old sins have long shadows	old skool
the old sod	old soldier
stamping ground	old stick
old story, an	old trout
war horse	old warhorse
old windbag	old wives' tale
oldbie	older
older adult	older brother
older sister	olde-worlde
oldie	oldie but goodie