The health-care sector has been en fuego for the past several years, fueled by robust sales and profits among biotechs, big pharma and medical services providers. And health care-related exchange-traded funds have gotten a boost from another source—baby boomers who are following legendary fund manager Peter Lynch’s maxim to invest in what you know.

According to recent client data from TD Ameritrade, investors ages 56 and up are more apt to invest in health-care-related ETFs because the industry is more relevant to their lives. “Boomers are more familiar with these companies, as they are taking more medications than millennials,” says Alex Teyf, TD Ameritrade’s director of mutual funds and ETFs.

And boomers in general seem to be taking a shine to ETFs. During the past 24 months (as of May), TD Ameritrade had seen a 20% increase in accounts that had a 50% increase in assets under management within ETFs for clients nearing retirement. “Those over 65 are turning to ETFs for their efficiency, cost, exposure to emerging markets and diversification of their portfolio,” Teyf says.

While ETFs are growing in popularity, Teyf notes they won’t be overtaking mutual funds anytime soon because actively managed funds continue to see inflows. “Mutual funds make sense in actively managed portfolios and passive portfolios when clients are eligible for institutional class shares that are sometimes less expensive than the ETF,” he says. “Clients with higher balances have greater access to these mutual fund products.”

That said, Teyf doesn’t believe mutual fund companies will let the booming ETF market eat its lunch without a fight. “Every mutual fund company I speak to that doesn’t yet have an ETF has told me they are looking at the space and will make an entry when there’s an opportunity for them to gain market share there,” Teyf says.

Indeed, a number of mutual fund companies have been kicking the tires about possibly entering the ETF space, but so far it’s been more speculation than reality. Meanwhile, ETFs continue to grab inflows from young and old investors alike.

“Our study validates the ETF as a product that has hit its stride and isn’t stopping,” Teyf says.