MARSHALLTOWN, Iowa (AP) — Bernie Sanders insists he feels better than ever less than a month after heart surgery, but his return to the campaign trail this week sparked new questions about the unusually old age of the Democratic Party’s leading 2020 presidential candidates. The 78-year-old Sanders and 76-year-old Joe Biden suggest their age isn’t a major issue. But voters, particularly older voters, aren’t so sure.

Gordon Lundberg is a 71-year-old retired Lutheran pastor from Ames, Iowa. He says candidates’ health is a key issue for him because he understands how it feels to age. He’s leaning toward Elizabeth Warren and says even though she’s 70 “she’s the most liberal and she’s not got one foot in the grave yet.” Lundberg says Sanders and Biden are “just too darn old.” Lundberg is not alone.

Polling has suggested that a significant number of Americans believe a candidate in his or her late 70s is too old to be president. If elected, Sanders would take office having already exceeded the average U.S. life expectancy of 78.6 years, according to data from the Centers for Disease Control and Prevention’s National Center for Health Statistics. Biden would be just a few months away. Sanders would be 79 years old when inaugurated. Biden would be 78 if he wins. To date, Trump is the oldest candidate to win a first term: He was 70 when sworn into office.