Earlier this month at the Metropolitan Opera Plácido Domingo added a new role to his vast repertoire, the title character in Verdi’s “Simon Boccanegra.” Domingo just turned 69, and made his operatic debut back in 1961, almost 50 years ago. The tenor, now singing this Verdi baritone role, has had one of the longest, most varied singing careers in history.

It’s a rare classical singer who can keep continue to perform leading roles for more than perhaps two decades at the most. It takes a while for the classical voice to settle – often into one’s 30s – but then too quickly the voice ages, tires, and after decades of nurturing and coaxing the singer might decide not to tax what’s left of his instrument.

Sometimes the voice simply gives out. But Domingo, who has been blessed with a particularly strong vocal constitution (among other strengths), is a relative rarity. (Many would argue that one of Domingo’s Three Tenors colleagues, Luciano Pavarotti, kept singing for far too long.) But Domingo’s endurance at the top tier of singers for so many years led me to wonder about the length of the professional career of other singers, both in the classical and pop realms.

Some singers have had remarkable careers cut short by tragedy, of course. Fritz Wunderlich, the great German tenor who specialized in Mozart (but who might have moved on to Wagner) died at the age of 36 in a freak fall from a staircase. Lucia Popp, the Slovak soprano, had an outstanding voice that combined great purity with exceptional passion – she was a fiery Queen of the Night in the famous Otto Klemperer recording of Die Zauberflöte from the early 1960s, and gave a wrenching performance on her record of Strauss’s Four Last Songs. She was concentrating on recitals as her career entered its third decade but she died of bone marrow cancer at the age of 54.

Even Kirsten Flagstad, considered one of the great sopranos of the 20th century, had a career that lasted about 25 years (she died of cancer, too, at the relatively early age of 67 in the early 1960s). She thrived in the 1930s and 1940s, but made several lustrous recordings into the 1950s; these showed some deterioration of her clean unforced vocal line, but no diminution of her expressive power. And she did sing the premiere of Strauss’s Four Last Songs in 1950, in what was considered a masterful performance.

Longevity is a matter of genetics, of course, as well as technique. Opera lovers have long debated the decline in Maria Callas’s voice, tracing it to her weight loss (80 pounds in 1954) or to her decision to sing too early in her career either – flip a coin –the heavier dramatic roles such as Wagner or the lighter bel canto ones. In any event, her voice had declined by the 1960s (some would say the late 1950s), and this sublime artist had perhaps only a decade of prime singing on world stages (but what a decade). She died at the age of 54 of a heart attack.

There are long careers in pop, too. Frank Sinatra sang in public for five decades. Tony Bennett is still going strong, and sounding excellent, at 83. Pop singers have an advantage over opera singers because they rely on microphones rather than having to project to the rafters, over an orchestra, on the strength of diaphragm technique and lung capacity.

You could argue that because Bennett uses a microphone, he’s been able to keep producing a smooth sound longer than the unaccompanied voices of opera singers. But Bennett is still given to letting his unamplified voice ring through a concert hall – part bravado for an octogenarian showman, part thrill at his still being able to let loose.

And pop singers can also count on their dramatic chops to put songs across when their singing abilities diminish. Think of Elaine Stritch, who was never a singer with a beautiful sound (though she did have a strong voice in her day), who now talk-sings, to great effect, during her cabaret appearances. No less a judge of vocal talent than James Levine has caught her recent performances at the Café Carlyle in New York.

Musicianship is musicianship, in whatever sphere. The lucky classical singer such as Plácido Domingo can continue to command an operatic stage into his seventh decade on earth. Some lucky classical singers can move toward the recital hall and extend their careers, as Jessye Norman, among others, has done.

In February, Renee Fleming turns 51, and in August, Deborah Voigt turns 50. These are two of the leading sopranos in the world. And they’re still singing strong. One can never predict how long a singer will last, but these two sopranos have taken care of their voices. Voigt has lost a considerable amount of weight, but has been careful about her technique as she’s slimmed down. One hopes these artists will be around for a long time.

There’s no shortage of singers, of whatever skill. But great singing is rare, and it would be a shame for any fine singing career, popular or classical, to be cut short. We can never have too much vocal music in our lives.