old hand at something

an old hand

One who has experience doing a particular task. If you have any questions, ask Andrea—she's done this job before and is an old hand at filing. I've been a bus driver for seven years, so I'm an old hand at this.
See also: hand, old

old hand (at something)

n. someone experienced at doing something. I’m an old hand at fixing cars.
See also: hand, old, something