A chip off/of the old block
- a son or daughter who is very much like his or her father in character or temperament
"He is just as stubborn and short-sighted as his father." "Oh, yes, he’s certainly a chip off the old block."
An old flame
- someone of the opposite sex to whom one was strongly attracted at some time in the past
Chris ran into Amanda in a restaurant yesterday. She’s an old flame of his from their student days at Oxford.
An old fogey
- an elderly, narrow-minded person who is out of touch with modern thinking
You can call me an old fogey if you want, but I think that young people today are totally misguided.
An old hand at something
- someone with a lot of experience and practice at (doing something)
"I need someone to help me fix these shelves." "Well, ask Tom. He’s an old hand at that sort of thing."
Old hat
- out of date, no longer original, topical or fashionable
"What did you think of the lecture?" "Well, quite honestly, most of it was old hat!"
The old man
- a term used for a father or a man in authority over a group of employees etc.; e.g. a firm’s director, a headmaster
Oh, by the way, I just saw the old man. He wants to see you in his office immediately.
The old school
- traditional thinking/standards/code of behaviour as in former times, as opposed to modern thinking
Our history professor is one of the old school. He expects us to be the same as students in his day.
Any old how
- in a careless, bad manner
Tony doesn’t care what his homework looks like. He does it any old how.
For old times' sake
- for sentimental reasons related to pleasant memories from the past
I spent my childhood in Leeds. I'd like to go back there one day - for old times' sake.