ORLANDO, Fla. — For pooches and the people who love them, one of life’s great injustices is that dogs grow old too soon. A 7-year-old is already a “senior.”

Thousands of them languish in animal shelters across the country, passed over by humans fixated on the young and cute. Laura Coffey, writer, editor and producer, finds it heartbreaking.

“These dogs should be treated with kindness at the end of their lives,” said Coffey, author of the recently published book “My Old Dog: Rescued Pets with Remarkable Second Acts.” “When you adopt one, it’s a relief for everyone. It’s a relief for the dog to be in a home. And it’s a relief for the person because you know you’re doing something good.”

Cullen, a 10-year-old black Lab adopted by a Chuluota, Fla., woman, had been trained as a service dog by Canine Companions for Independence and spent years serving an Orlando, Fla., polio survivor — until he could no longer pull her wheelchair. But in his new home, he has flourished, working as a therapy dog at Nemours Children’s Hospital and getting to visit his former owner.

“It was this awesome scenario,” Coffey said. “He loves his new job.”

Coffey, who has two senior dogs, stumbled onto this subject in 2013 when she did wrote a story on Lori Fusaro, a Los Angeles photographer who was then volunteering to photograph shelter dogs. Fusaro’s portraits aimed to show more of a dog’s personality. She was troubled that so many older shelter residents still seemed destined to spend their final days alone, facing the likely prospect of being euthanized. She ended up taking one home: a 16-year-old pit bull named Shady, who had cancer.

She changed the dog’s name to Sunny, got her some veterinary care — nothing heroic, Fusaro says — and watched Sunny live joyously for nearly three more years.

Coffey’s main mission is to help people see how an old dog can love anew.

“And when it comes time to say goodbye, there’s something about having given them a safe and happy final chapter that softens the hardest part,” she said. “Let’s face it, for any dog of any age, when the end comes it’s always too soon.”