NEW YORK — Retiring comfortably at 65 is now out of reach for millions of Americans. Tom Coomer was a machinist at the aerospace manufacturer McDonnell Douglas for 29 years, but the plant closed one year before he was due to get his full pension. Now 80 years old, he works as a greeter five days a week at a Walmart in Oklahoma.

While Coomer and his wife have downsized their lifestyle, it's still hard for them to make ends meet. They're just two of nearly 10 million Americans still working past the age of 65.

According to CBS News business analyst Jill Schlesinger, Americans are facing three main obstacles to retirement. They're living longer, median wages have stagnated over the past 20 years and a shift from pension plans to 401(k)s have all put a burden on employees.

But the National Bureau of Economic Research has found that working longer by even a short period of time can have a dramatic impact on retirement. For example, retiring at 66 instead of 62 can increase the standard of living in retirement by almost 33 percent.

"Hang in there until age 70, and your standard of living will improve nearly 75 percent," Schlesinger said.

That delay allows workers to contribute to retirement plans while allowing savings and investments time to grow. By waiting to file for Social Security benefits, workers will also see a larger monthly check once they do retire.

But Schlesinger acknowledges working longer isn't an option for everyone. Health issues, disability or becoming a caregiver may take over that primary job. And like Coomer, some workers who want to work longer may be faced with downsizing by their company.

"Anyone who right now can work and can put away some money, it's all the more important to do so as early as you possibly can," Schlesinger said.