71 is too old to work. No, it's not.

My Pop retired the other day. He's been hobbling toward that inevitable outcome for a while now, but up until this year, he was still making the one-hour-plus commute by train to his ad agency up to three times a week. After a hospital stay weakened him, however, the commutes became untenable. So the other day, my older brother George drove him into the office, where Pop said his good-byes and cleaned out his desk.

Pop is 75. That's how old John McCain would be when he completes his first term as President of the United States, should he get the chance. I think of this because of the debate raging about his health (see this article in TIME by my colleagues Michael Scherer and Alice Park) and—perhaps more pointedly—about his age.

And so I'm wondering: is 71 too old to work? I think not. Thinking back, my father was almost sprightly four years ago. The long, crowded commute on Japanese trains was beginning to wear on him, but the mental stimulation of dreaming up ad slogans, rewriting copy and meeting with clients was worth the haul. He always proclaimed to wake up every day excited to go to work. I can't even say that now, and I'm less than half his age.

No, 71 isn't too old to work. But it might be too old to lead. Pop ran the small ad agency he'd founded for nearly 40 years, but he had the foresight to hand off the reigns years ago to his longtime business partner. Having a solid succession plan in place allowed him to keep working till 75—without the stresses of leadership.

I don't think John McCain is too old to be President—right now. But I know from my dad that four years can do a lot to a man, even if those years weren't spent in the toughest job in the world. Unless someone comes up with a way to stop him from aging, I think McCain will soon be too old to lead. (Go on. Debate.)