Zaid Jilani is a Bridging the Divides Writing Fellow at UC Berkeley's Greater Good Science Center. He is also a long-time political journalist who is the co-host of the podcast Extremely Offline, which brings together guests from competing political tribes for civil dialogue. Follow him on Twitter at @ZaidJilani . The opinions expressed in this commentary are solely those of the author. View more opinion at CNN.

(CNN) Vice President Joe Biden is now officially running for president in the Democratic primary. For many voters, his candidacy raises a question: Should we choose someone who could potentially be the oldest president the United States has ever elected?

Biden is 76 years old, just a year shy of Vermont Sen. Bernie Sanders, another contender. Upon inauguration, both Biden and Sanders would be older than President Donald Trump, who was 70 when he took office in January of 2017.

At first glance, voters don't seem to mind. Biden and Sanders are the top contenders in national polls , and both are widely considered front-runners for the Democratic nomination.

But below the surface, age concerns do appear. A poll from the University of New Hampshire found that 49% of Democratic-leaning primary voters were "somewhat" or "very concerned" about nominating a candidate over the age of 70. By comparison, only 38% held similar concerns about nominating an openly gay candidate, such as former South Bend, Indiana, mayor Pete Buttigieg.

Earlier this year, Harvard researchers Tessa Charlesworth and Mahzarin Banaji studied data collected from 4.4 million tests of conscious -- or "explicit" -- bias against many different social groups, and compared that with measures of unconscious -- that is, "implicit" -- bias.

From 2007 to 2016, they found, conscious and unconscious bias toward numerous groups in America precipitously declined , including bias around sexuality and race. But there was one big exception: bias toward the elderly. Though conscious bias against older adults did decline over this period, unconscious biases barely shifted at all, suggesting negative attitudes that are deeply rooted in our culture.

It is perhaps no surprise, then, that some of the younger candidates are subtly emphasizing their age difference. "We're less interested in politics as usual and more focused on getting Mayor Pete's hopeful message of generational change out there," Lis Smith, a communications adviser working for Buttigieg's campaign said recently. Buttigieg is 37 years old.

For many voters, no doubt, age discrimination seems rational; they'd likely point to higher mortality rates among the elderly and concerns over mental competence.

But one of the building blocks of discriminatory thinking is taking mental stereotypes about a group and applying them to individuals. Sanders and Biden, like most top-tier presidential candidates, will likely do medical tests and release the results to the public. If voters base concerns on these individual results, they'll have avoided bias. But that's not the case if they're falling back on stereotypes about the elderly in general.

Judging older people based on crude group stereotypes has real-world consequences. In 2013 , researchers at Boston College used workplace data gathered from the Sloan Center's Age & Generations study and found that "negative attitudes toward late-career workers do in fact affect these workers' engagement with their jobs and ultimately their mental health."

The researchers warned that age-related epithets such as "geezer" and "old bag," as well as assumptions about the capabilities of the elderly, can be truly harmful -- they "affect older workers in the same way that they do members of racial minorities, eroding self-esteem."

The researchers suggest that employers take affirmative steps to support elderly workers, including engaging in team-building that emphasizes inclusion of older employees. They note that when older workers are able to maintain their engagement in their jobs and enjoy them, they are more likely to stay with the company and reduce the cost of having to recruit and train newer employers.

When we see political columns that argue that "Joe Biden and Bernie Sanders are too old to be president," the title of a piece by the Washington Post's Richard Cohen, what we are seeing is an embrace of the same flawed mental shortcut -- judging an individual based on stereotypes about their group -- that leads to the degradation of all older workers, not just those running for president.

So how can we break down barriers between the young and old? We know that contact between members of different groups -- particularly under certain conditions, like when the participants have a sense of equal status -- is one of the best ways to improve the attitudes that those groups have toward one another.

Organizations like Encore.org do just that. Encore's Gen2Gen program promotes intergenerational relationships by helping organizations recruit older Americans for volunteer and job opportunities that involve working with and mentoring younger generations.

In the political arena, the Sanders campaign already modeled how to create an intergenerational movement. In 2016, the Vermont senator won more votes from young people during his primary campaign than Donald Trump and Hillary Clinton combined. The campaign proved that young people could overcome social bias against the elderly to support someone who could go on to become the country's oldest president. In 2020, his base may end up being similarly young

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That bridge-building talent may bode well for Sanders, especially in a political environment where many candidates are pitting different social groups against each other. Can we all grow to recognize that we are engaged in flawed and discriminatory thinking when we argue that someone is "too old to be president?" Can we apply that self-awareness to our own workplaces when we make hiring decisions? Time will tell.