"You don't get people for as long," Cilman said. "You get really fond of people and then they get sick or die. There's the fact you can't have these people forever."
Two members passed away during the filming of the documentary. Cilman remembers one such member, a beloved man named Joe Benoit who died of cancer, as an example of the passion and devotion of Young at Heart's members.
"That guy was really sick for a long time and he just ignored every doctor's advice to be part of this thing, and to sing and go on tour," Cilman said. "He was in London for thirteen shows in two weeks, it was amazing. And that was four or five months before he died."
Said one member of the group: "You have to expect it. You don't feel bad about it. Face facts. Get real."
But their resilience doesn't mean the feelings aren't deep. The group gives an unparalleled poignancy to the old theater phrase "the show must go on."
In the film, for example, longtime member Bob Salvini is enlisted to sing a duet of Coldplay's "Fix You," but passed away just weeks before the show. It left 82 year-old Fred Knittle, who is on an oxygen tank, to sing it on his own. What resulted was a truly moving rendition of the song, whose lyrics are about helping someone to get over grief, in which Knittle's oxygen tank acted almost like an additional musical instrument.
"I love that he has that oxygen machine as a rhythm box," Cilman said. "I think it's one of the most incredible moments. You know it's not anything we really planned, but if you listen to it in the movie, it's just haunting."
The video of Knittle performing "Fix You" has received more than 600,000 hits on YouTube.
"Young at Heart" tackles issues of loss and the pervading sadness of old age, but the film is also very much about life. Cilman says his favorite scene is at a prison, when the chorus goes to entertain the inmates.
"Here's people who are stuck in this place," Cilman said. "Some of them won't get out till they're old and they probably figure their life is completely over. And the idea of these people walking in and saying you know what, till the day you die there's something that can be interesting in your life. And I think that's what happened there."
Until the day you die there's something that can be interesting in your life; that is what Young at Heart is about. And that is why everyone from jailbirds to journalists can't help but smile when they watch.
"Hopefully, you're smiling because you're enjoying it and it's good," one member said. "The worst smile is that ''Isn't that cute?' sort of smile, like, 'Isn't it sweet that these people are doing this?' thing. We're not interested in that at all. We're interested in people coming there and saying 'Wow, this is good. I dig this.'"
The group relishes the element of surprise in its act. "They don't expect us to sing rock in the first place," said Lenny Fontaine, 87, who sings the lead on "Purple Haze." In the second place, they say 'Well those are people who are not sitting down on their haunches and not being a sofa person."
There seems to be no danger of anyone in the Young at Heart chorus becoming a "sofa person" anytime soon.