Modern medicine is enabling retirees to live longer than ever. That's wonderful news for humanity, but it also means that older investors will be relying on their nest eggs for much longer. That's why we Fools believe that all retirees should keep at least a portion of their portfolios invested in the stock market.

Of course, not every stock is a good choice for retirees. Older investors should focus on buying strong companies with good growth prospects for attractive valuations. Knowing that, here's why I think that Medtronic (NYSE:MDT), Synchrony Financial (NYSE:SYF), and Skyworks Solutions (NASDAQ:SWKS) are all solid choices for these investors to consider today.

An older couple holds fans of money in front of their faces.

Image source: Getty Images.

The low-risk option

Learning how to use a medical device takes quite a bit of time, so when healthcare providers become comfortable with a product, they tend to stick with it. That fact provides the goliath of the industry -- Medtronic -- with a wide and enduring moat that other companies have found hard to breach.

Medtronic's business is divided up into four business units: cardiac and vascular, minimally invasive therapies, restorative therapies, and diabetes. The company boasts a strong competitive position in each of these areas, and it has a long history of using its financial might to make smart acquisitions. The company's knack for developing or acquiring industry-leading products has helped its revenue and profits to tick continuously higher for decades:

Looking ahead, Medtronic has made a number of deals over the past few years that should allow this trend to continue. Beyond its megamerger with Covidien in 2014, the company also recently signed a deal with Mazor Robotics to partner in the fast-growing robotic-surgery market. The company also struck up a deal with Fitbit to help patients with type 2 diabetes better track and manage their disease.

With these moves and the expected increase in demand for healthcare services, Medtronic's 39-year history of consecutive dividend increases looks poised to continue indefinitely. With shares trading for 16 times forward earnings and offering up a dividend yield of 2.1%, Medtronic is a low-risk stock that should produce slow but steady gains from here.

A little more risk, a little more upside

Nearly every investor is familiar with credit card issuers such as Visa, MasterCard, and American Express, but I'd bet that few have ever heard of Synchrony Financial. This company was spun off of General Electric a few years back, as the industrial giant was looking to get out of the financial industry completely.

So what does Synchrony Financial do? This company runs private-label credit card networks for retailers such as Lowe's, Gap, Wal-Mart Stores, and more. Retailers love providing customers with these cards since they encourage loyalty, provide the companies with valuable data, and let them avoid hefty fees from other credit payment networks.

With retailers pushing these cards like crazy, Synchrony now has more than 68 million customer accounts in its network. The company has also benefited from the general rise in consumer spending over the last few years. In turn, customers are carrying higher balances, which is allowing the company's revenue and profits to rise consistently.

Consumers' love of credit isn't going away anytime soon, and retailers will likely continue to push private-label credit cards in an effort to deepen their relationships with customers. As long as this company can control its credit quality, Synchrony should be able to drive steady revenue and profit gains in the coming years. With shares trading for less than 11 times forward earnings and offering investors a yield of 1.4%, Synchrony Financial offers potential shareholders growth for a value price.

Higher-risk, high reward

As a manufacturer of specialty semiconductor chips, Skyworks Solutions might seem to be a head-scratcher of a choice for retirees. After all, the semiconductor industry is ruthlessly competitive and known for its cyclicality, which makes it a tough place to invest. However, I think that Skyworks Solutions is well positioned to continue to shower investors with rewards.

Skyworks Solutions supplies chips for a wide range of products, but its bread and butter right now is the smartphone market. The company's highly complex and integrated chips can be found in top products on the market such as the Samsung Galaxy and Apple iPhone. Exploding consumer demand for these smartphones has allowed Skyworks' revenue and profits to soar over the last few years, driving big returns for shareholders.

Even though the smartphone market is maturing, I don't think Skyworks' growth story is over yet. The company is pushing hard to become a big player in the "Internet of Things" (IoT) trend, with product wins in growth markets such as automotive, home automation, industrial, and machine-to-machine communications. As consumers and businesses demand more connected devices, Skyworks' financials should flourish.

Another upcoming catalyst for sales growth is the 5G wireless rollout. Carriers are poised to start investing heavily in 5G connectivity, which should drive a massive smartphone upgrade cycle.

Given the company's leadership position in its industry and trends at its back, market watchers expect Skyworks profits to rise by more than 14% annually over the next few years. With shares trading for less than 14 times forward earnings and offering a modest dividend yield of 1.2%, I think this is a growth stock that even conservative investors can learn to love.