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"Happy Birthday" song

Tess Vigeland: 75 candles on the cake! Happy birthday to Social Security. On Aug. 14, 1935, FDR signed into law the Social Security Act -- also known as Old-Age, Survivors, and Disability Insurance. The first person to receive a check was a Cleveland retiree named Ernest Ackman. His lump sum payment? Seventeen cents. Well today, more than 58 million people receive some sort of benefit from the program. For many of them -- it is their only income.

Peter O'Dowd of station KJZZ in Phoenix has a glimpse into their lives.

Peter O'Dowd: Last year, the Social Security Administration paid out nearly $700 billion to elderly and disabled Americans.

Richard Kepner is one of them.

Richard Kepner: Good morning, welcome to the Banner Olive Branch Senior Center for lunch. My name is Rick, and I hope you're all doing well.

Kepner is preparing the lunchtime announcements at this senior center in Sun City, Arizona's most famous retirement community.

Kepner: Now you know we need it quiet so you can hear me. Please!

Kepner is 62, and he wants you to hear what it's like to survive on nothing but a pair of bad knees and a Social Security check. Every month, the U.S. government sends Kepner $1,300.

Kepner: It's not enough. I mean, I'm behind the eight ball each and every month. Being disabled, I'm unable to really work. I have certain fixed bills that I have to pay. It's just been a struggle.

Every month, Kepner pays home owner's fees, mortgage payments, utilities. He takes a $300 advance from Social Security before his check is even cut. Sometimes, he has to ask the Olive Branch Senior Center for help paying his mortgage. Kepner used to be an accountant. Yet, he never bothered to save.

Sound of cue stick hitting pool balls

I traveled across town to the Devonshire Senior Center to see if the situation of people like Kepner is unusual. It isn't.

Annie Monrad: I'm Annie Monrad, and this is my favorite pastime, being here at Devonshire, shooting pool.

Sound of cue stick hitting pool balls

Monrad is 73 years old. She has a bachelor's degree and a master's in linguistics, but she tended bar for most of her working life.

Monrad: I live on Social Security. I get $1,040 a month. So I don't turn on my air conditioner. I'm dying of heat.

Monrad told me she thought she'd live forever. She saved a little, but she admits she was completely unprepared for retirement. At the end of each month, she has nothing left.

Monrad: My life is very very different. You inexpensive food, you don't go any place. So all I can do is be as cautious as I can about the money I spend and hope that it's enough.

I met a few others at the Devonshire Senior Center, and the stories were similar. AARP estimates 14 percent of the elderly rely solely on Social Security. The manager of the Olive Branch Senior Center in Sun City says half of her members have no other source of income.

Sound of someone playing piano

I met one of the residents, Suzie Roberts in the dining room at the Olive Branch. The room was bright and the music cheerful, but that masked the fragile existence of so many people here.

Suzie Roberts: I never resented paying into Social Security, because I knew it would be a buffer when I got older. I didn't realize I was going to end up relying on it.

But just like the others, Suzie Roberts now depends on the government. Every month, Uncle Sam sends the former office manager 1,000 bucks. Almost half of that pays for medication to keep her alive. Roberts splurges on a perm twice a year. She shops at thrift stores for used clothes.

Roberts: What you see is what you get. If you're looking for a rich old lady, you ain't gonna get one.

This 74-year-old woman has a sweet smile, but she knows this isn't funny. Without Social Security, she says she'd be homeless.

Roberts: I would be stuck in some corner some place. My children can't afford to take care of me. They have families. The Olive Branch is my main stay... I'm sorry, I get emotional.

Roberts' advice: Save -- and save now. Because she believes the next generation will face similar problems. The government predicts Social Security will begin to falter by 2037. By then, tax revenues will only pay for 75 percent of scheduled benefits.

Seniors singing "God Bless America"

Roberts composes herself before moving to the dining room where Richard Kepner is leading the group in song. When he's done, 100 people will eat a free plate of breaded cod and mashed potatoes.

In Phoenix, I'm Peter O'Dowd for Marketplace Money.