You could forgive Shirley Williams Myrie for not recalling the details of her first day on the job.

When the 82-year-old — who is believed to be the longest-serving active city employee — first reported for work on Nov. 2, 1953, Casey Stengel was managing the Yankees, Eisenhower was president and it would be eight more mayors before Bill de Blasio took office.

“I’ve known people who retired — now they have walkers, they have wheelchairs, canes — and I said I don’t want to end up like that,” Williams Myrie told The Post. “I want to do something to keep busy.”

Hired at age 18, Williams Myrie has worked for what is now known the Administration for Children’s Services for the past 64 years.

She hasn’t even left the legal department in which she started on day one.

“They wouldn’t let me go! I almost went to another location . . . but at that time, the general counsel heard about it. He intervened,” said Williams Myrie.

“He called up personnel, and said ‘No, we can’t let her go. She’s gotta stay.’ ”

A graduate of Theodore Roosevelt HS in The Bronx, Williams Myrie said she was first hired as a stenographer in what was then known as the Department of Welfare under Mayor Vincent Impellitteri at a salary of $2,650 — “per year,” she notes. “Not per month.”

She said she maintained an interest in her work by bouncing from issue to issue — from contracts to child protection, and from criminal cases to correspondence — and by having a natural affinity for her colleagues, many of them lawyers who offered her encouragement.

Williams Myrie said the job search in the 1950s hadn’t been easy, and recalled being overlooked as the lone African-American woman in the waiting room at private firms — while other candidates responding to advertised positions breezed in and out of interviews.

After being hired by the city, she moved up the clerical ladder to her current title of principal administrative associate III — the top position.

Over the years, the division dealing with children went through a number of iterations, until then-Mayor Rudy Giuliani separated it out as ACS in 1996.

While Williams Myrie said the impact of a mayor on her day-to-day job was minor, she still has her favorites among the eight elected since she was hire.

“I liked [David] Dinkins, I liked [Ed] Koch and I liked [Robert] Wagner,” Williams Myrie said. “Giuliani, his mannerisms. He was sort of, not rude . . . I have to say rude sort of.”

While a lot of small things have changed in Williams Myrie’s work life — she remembers the manual typewriters made by Royal and Olivetti, and the labor-intensive mimeographs that preceded copying machines — she hasn’t greatly altered her routine.

She still commutes roughly an hour each way from The Bronx by subway, bus and foot — and takes the stairs rather than elevators.

She still uses the post office that’s farther away from the office to send work documents, because the one nearby doesn’t send packages out quickly enough.

And at home, Williams Myrie still lives with a niece she raised like a daughter, and one of her two sons lives in an apartment downstairs.

Her husband, Raymond Myrie — a former postal worker — died in 2005.

While she said she’s considered retirement, Williams Myrie said she doesn’t have plans to leave the job any time soon. She likes to watch TV and go for walks in her free time, but she doesn’t want those activities to become the main parts of her day.