This year is turning out to be one of the best ever for Intuitive Surgical (NASDAQ:ISRG). Shares of the robotic surgical systems maker are up more than 60% so far in 2017. There hasn't been one big catalyst for Intuitive Surgical. Instead, the stock has steadily risen throughout the past nine months.

Its momentum could just be getting cranked up. There's a long-term trend that definitely works in Intuitive Surgical's favor: Americans are aging. For that matter, so are the populations of many industrialized countries. Here's why this trend makes Intuitive Surgical stock an awesome buy.

Doctor at controls of da Vinci robotic surgical system

Image source: Intuitive Surgical.

The older are getting older -- and so are the young

You've no doubt heard plenty about the impact of the the baby boomer generation reaching their retirement years. The first baby boomers turned 65 in 2011, while the last of the generation hits the milestone 12 years from now. The following chart shows what that means in terms of the number of Americans ages 65 and over.

U.S. population age 65+ chart

Image source: U.S. Census Bureau. 

The steep upward trajectory on the chart through 2030 reflects the direct impact of baby boomers aging. This trend is also present in many other nations.

Percent of population age 65+ in 2015 and 2050 maps

Image source: U.S. Census Bureau. 

While a lot of attention has been placed on the aging of the baby boomer generation, there's another perhaps more significant impact of the U.S. population aging. Millennials, which comprise people born between 1981 and 1997, is actually the biggest generation ever in the U.S. The oldest members of this generation are now 36 years old and nearing middle age. 

Why these trends especially help Intuitive Surgical

Higher numbers of older individuals help many, if not most, companies in the healthcare industry. That's because the elderly tend to require greater medical care and use more prescription drugs. For Intuitive Surgical, the aging of the baby boomers is especially helpful.

The second-highest procedure performed with Intuitive's da Vinci robotic surgical system is radical prostatectomy -- removal of the prostate and some of the tissue around the organ. As you might expect, prostate cancer ranks as the primary reason why radical prostatectomy could be necessary. According to the American Cancer Society, the average age for diagnosis of prostate cancer is 66.

Intuitive Surgical should see significantly higher numbers of patients requiring radical prostatectomy in the near term as well as the long term thanks to the aging demographic trends. Growth in this procedure translates to growth in sales of instruments and accessories. These sales currently generate over half of Intuitive Surgical's total revenue.

The company's da Vinci system was used for nearly 190,000 general surgery procedures in 2016. The American College of Surgeons predicts that "the aging of the population will lead to a significant increase in the demand for surgical services." Increasing numbers of older patients should also mean higher procedure volume overall for Intuitive Surgical. 

Intuitive Surgical won't just benefit from an increased elderly population, though. The aging of the millennial generation also presents opportunities for the company. Currently, the most-performed procedure with the da Vinci system is hysterectomy. The average of women getting hysterectomies is 42. Within the next six years, the biggest generation in U.S. history will beginning hitting this average age, which indicates a strong probability that Intuitive Surgical will experience significantly higher demand for its top procedure in the future. 

But what about...

There are two key questions that investors will most likely raise about Intuitive Surgical. One relates to competition. The company wouldn't be able to reap the rewards for the long-term aging trend if another rival swoops in with a much better product.

In fact, increased competition is on the way. Medtronic (NYSE:MDT) plans to launch its robotic surgical system next year. The large medical device company intends to target all procedures currently performed by robots. Medtronic already claims relationships with many of the hospitals that use da Vinci and others that Intuitive Surgical would consider as prospective customers.

The other question is about Intuitive Surgical stock's valuation. Intuitive shares currently trade at nearly 38 times expected earnings.

I'm not overly concerned about either of these issues. Customers that already have da Vinci installed aren't likely to throw away a system for which they've spent a lot of money to implement. Intuitive Surgical will also have a good shot at beating Medtronic for new customers due to its established track record.

As for valuation, the reality is that Intuitive Surgical stock has been more expensive in the past than it is now -- and still went up. Even with the stock near all-time high levels, I think the long-term demographic trends make Intuitive Surgical an awesome buy for the long run.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.