ROME – Pope Francis yesterday celebrated his 86th birthday, which makes him the first pontiff in over 100 years to reach that milestone while still in office. Pope Benedict XV’s reign ended in 1922, when he was 67, and over the century since the average age at which popes have either died or resigned has been 78.

During the entire last millennium, the span for which we have reliable records of papal birthdates, there’s been a total of 123 popes, and only six have remained in office past their 86th birthday. Prior to that documentation is sketchy, but the lone pope of the first millennium who, by reputation anyway, was older in office than Francis is now was Pope Agatho, who was supposedly 104 at the time of his death in 681.

In other words, it’s possible that out of 266 papacies in church history, Francis is now one of just eight – put another way, a statistically negligible three percent – to be 86 or older while still serving as Successor of Peter.

Conventional logic would suggest, therefore, that Francis’s birthday should be a moment for speculation about the end-game of his papacy. The striking thing today is how little of that sort of talk one hears – instead, the impression given by the Argentine pontiff is that it’s full steam ahead.

(Perhaps Vatican-watchers got the “end is nigh” fever out of our system over the summer, when Francis cancelled several activities, summoned all the cardinals to Rome for an unusual set of meetings and visited the tomb of the last pope to voluntarily resign before Benedict XVI – all, as it turns out, without giving up the ghost.)

In a new interview released today with the Spanish newspaper Abc, Francis repeats an old line when asked about his health, especially the arthritis in his right knee which has hobbled him periodically over the past year.

“You govern with your head,” Francis says, “not with your knee.”

“I’m now walking, so the decision not to have an operation was the right one,” he also tells the Spanish journalists, suggesting that he feels more or less good to go.

In the same interview, Francis also reveals for the first time that early in his papacy he signed a resignation letter in case of medical incapacity and gave it to his then-Secretary of State, Cardinal Tarcisio Bertone. Clearly, however, he’s not inclined to invoke it yet.

Proof of the point, perhaps, is that in early December the Vatican officially confirmed the dates for his Jan. 31-Feb. 5 trip to the Democratic Republic of Congo and South Sudan, a demanding overseas outing that the pontiff was forced to postpone in July.

Francis certainly doesn’t give off many signs of winding down. Over the last few weeks he’s orchestrated a major shake-up at Caritas Internationalis, the umbrella group for Catholic charities worldwide, and also made several key personnel moves, including new leadership for the Secretariat for the Economy. Vatican sources with knowledge of these developments say they weren’t a matter of someone else acting in the pope’s name – Francis himself, they say, was the prime mover.

In addition, Francis already has an ambitious agenda for 2023.

The year will bring a summit of prelates in Rome in October as part of the pontiff’s “Synod of Bishops on Synodality,” a process now scheduled to conclude with another gathering in October of 2024. By all accounts Francis views the synodal process as a cornerstone of his legacy, and appears determined to see it through to the end.

In terms of travels, Francis probably will want to make up a trip to Lebanon that he was forced to postpone last summer. Barring the unforeseen, it also seems likely he’ll travel to Lisbon, Portugal, in August, for World Youth Day.

Francis is also intensely engaged in the diplomacy and geopolitics surrounding the war in Ukraine, most recently issuing an apology to Russia for having suggested that ethnic minorities allied with Moscow, such as the Chechens and Buryats, are responsible for the war’s greatest brutality.

The mea culpa seemed part of an effort to keep lines of communication with Moscow open, in a bid to help mediate a solution. Francis seems determined to keep that possibility alive, making it unlikely he’d contemplate walking away while the conflict is still raging.

There’s also implementation of the pope’s blueprint for Vatican reform, Praedicate evangelium, and the Vatican’s “trial of the century” for financial corruption, both of which Francis likely also would prefer to bring to completion.

All this is in addition to a primal truth about Francis: He seems to enjoy being in charge, and doesn’t appear at all anxious to call it a day.

In that light, perhaps the real speculative exercise about this papacy shouldn’t be when it’ll end, but how much longer it could go on. Admittedly, it’s deeply improbable Francis will go another 18 years and outlive Pope Agatho – frankly, I’m not even sure what odds you’d get on Francis being around another seven years and four months, thus breaking Leo XIII’s modern record as the oldest reigning pontiff.

On the other hand, improbable isn’t the same thing as impossible – and if you haven’t realized by now that with Pope Francis, anything is possible, then you just haven’t been paying attention.