It’s commonplace around firehouses to see firefighters transition to new career paths after two decades of service.

But usually, first-responder crews watch people walk out their doors when they hit about 50. Very few walk through the door fresh to firefighting.

At age 53, however, D.C. fire department paramedic Carmen Hackett is doing that: She graduated Friday as the most senior member and the only paramedic in Firefighter Recruit Class 388.

“I was the oldest person in the class, even older than the instructors,” Hackett said. “I was being taught by people who I am old enough to be their mother.”

No lifelong dream lay behind Hackett’s decision to put herself through the often grueling four months of training to learn the science of fighting fires and rescuing people. Her decision flowed from a decision to go after promotion opportunities that would come with adding firefighter to her skill set.

Hackett had been a city EMT since 1999, and for five years took the test to be a paramedic but failed each time — until last fall, when she received weeks of one-on-one instruction from the department’s lead paramedic instructor to finally earn the certification.

Firefighter training was the next challenge, with its physical demands of throwing up ladders, pulling hoses heavy with water and breaching locked doors — all while wearing at least 75 pounds of gear.

The strains push many to the limits of their endurance and some out of the program, said Capt. Jeffrey Patton, who supervised Hackett’s recruit instruction class. But each step of the way, Patton said, Hackett surprised her instructors.

“She wanted to do it. She had the fortitude and the will. We have people half her age who can’t do it,” Patton said. “She’s 53 and I’m 49, and I know how hard it is on my body. I give her the props.”

Over the past few years, the department has moved away from hiring firefighters, EMTs or paramedics who are certified only in a single role, and Hackett was one of the last. Of about 1,800 members, the agency employs only 37 civilian EMTs and 36 paramedics, officials said.

Hackett said it was “peer pressure” from friend Kim Shaw, a 19-year EMT for the city, that pushed her to show up at an orientation last fall, days after the paramedic exam, to become a firefighter.

“I was just so ecstatic to finally pass my paramedics exam. I was good. I was happy, I could finally sleep at night,” Hackett recalled. So, when Shaw suggested she take another step, “I said, ‘No! I’m good. I’m approaching 20 years [of service]. . . . I’m too old to go up and down firetrucks and go into burning buildings. No!”

But Shaw’s persistence won, with one pact between the friends: Shaw had to finish the training, too.

Unusual career changes are not new to Hackett.

The Newark, Del., native arrived in Washington in 1987 and crunched numbers on large procurement contracts for the General Services Administration. For about 12 years, she toiled behind a desk and grew to loathe the work.

So Hackett decided to go back to school to become an EMT, in search of a fast-paced job that helps people.

“I got tired of the sedentary lifestyle. It just was not exciting,” Hackett said. “I always wanted to do something in the medical field without having to go to a zillion years of medical school with student loans.”

At 33, she began as a District EMT in 1999. She worked in firehouses including Engine 30 on 49th Street, near the Shrimp Boat in Northeast Washington, and worked through most of the city with the exception of its upper Northwest. Her favorite assignment was working on the presidential unit that “followed the president around the city.”

In April, she joined her firefighter recruit class, beginning her days at 6 a.m. at the training academy, where the group ran through physical training for about an hour before packing the heavy gear and learning the craft.

“I never realized, being on the EMS side, how much firefighters really do and how physical it really is,” Hackett said. “You have to have a lot of upper-body strength. The equipment and gear is heavy. You have to have really good lungs.”

For the first five weeks, the 49-year-old Shaw, who grew up in Northeast Washington, ran next to Hackett each morning to encourage her. A medical issue forced Shaw to drop out of the class, but she continued each day to send Hackett a prayer and remind her that training wouldn’t last forever. Just until August.

“She cried some days, she was upset some days, but she pushed and pushed,” Shaw said. “She strived and she strived.”

And even during the toughest of times, Hackett had one more motivator at her Upper Marlboro home: her 13-year-old son, Colin Sampson, who is the family member who wants to become a tillerman on a ladder truck.

The rising eighth-grader said he reminded his mother that the work “looks like a fun job. You get to ride on a fireruck, put out fires and get to help others.”

Hackett expects an assignment to a fire engine company where she will treat patients as a paramedic and serve on a fire suppression team. She hopes her newest title will lead to a promotion to sergeant and eventually back to a desk job as an aide to a battalion chief before she retires in seven years.

Hackett still has unfinished business at the academy: encouraging Shaw, who has restarted her training.