Is it Phyllis Kahn being challenged, or her age?

Retirement age isn't what it used to be in America ­— or in American politics.

This nation's major parties just nominated a 70-year-old and a 68-year-old for the presidency, one of whom survived a vigorous challenge from a 74-year-old to win. Among the U.S. Senate's leading lights are Iowa's Chuck Grassley, age 82; California's Dianne Feinstein, age 83; Arizona's John McCain, age 79, and GOP Majority Leader Mitch McConnell, age 74.

At the Minnesota Legislature, the roster of House members seeking re-election includes DFLers Ron Erhardt of Edina, age 86; Lyndon Carlson of Crystal, age 76, and Phyllis Kahn, age 79.

Erhardt and Carlson will sail through the Aug. 9 primary with no intraparty opposition and are considered good bets for re-election to, respectively, a 12th and a 23rd term. If their GOP opponents are suggesting that they've grown too old for lawmaking, it's being said in a way that has made no blip on my reporting radar.

For Kahn, who is also seeking a 23rd term, it's another story. For the second time in as many elections, she's embroiled in one of the year's hottest legislative primary contests. The Yale-educated biophysicist and former University of Minnesota researcher was denied DFL Party endorsement, blocked by two young challengers from her district's large, politically stirring Somali-American community: newcomer Ilhan Omar, 33, and third-time candidate Mohamud Noor, 38.

Omar and Noor don't explicitly mention Kahn's age when asked why they want to unseat one of the two longest-serving legislators in state history. But that suggestion seems to lie just below the surface as they accuse Kahn of insufficient attention to her district and its needs.

"When you open the process to new people, you get rid of complacency, of the idea that says 'We've tried this already,' " Omar told the Star Tribune Editorial Board recently. "Our current representative has been quite complacent about a lot of the issues that matter to us. … We want to change, and our current representative isn't paying attention to that change."

For them, I'll attest that Kahn doesn't spend much time sitting at her House desk. More often she's prowling the chamber to ask colleagues on both sides of the aisle to cosponsor one of her many bills, chatting with staffers and reporters in the rear alcove, or standing with a microphone in hand, contributing to the debate of the day. Few House members are better versed on legislation or more frequently on their feet, sharing those verses with the body.

Yes, Kahn sometimes looks tired — after riding her bike 10 miles to the Capitol from her Nicollet Island home. And she may have been distracted from constituent service in the weeks after her husband of 58 years, University of Minnesota math professor Donald Kahn, died unexpectedly in 2015.

But Kahn-watchers noticed that not long after that blow, she dove into legislative work — perhaps finding it to be a source of solace. She introduced 51 bills in the 2015-16 lawmaking biennium, the 12th largest number among the 134 House members. All but four of those bills were introduced after her husband's death.

Some of us Kahn-watchers thought she might retire this year. She made sure we knew well before the March 1 precinct caucuses that she had no such intention.

Seniority translates into power at the Legislature — or at least, to a committee chair's gavel when one's party is in control. Kahn thinks the DFL might be back in charge of the House in 2017, and she wants the gavel back in the committee that oversees spending of the Legacy Amendment's sales tax proceeds, which are constitutionally dedicated to natural resources and the arts.

She disclosed that she has been thinking about leaving office one day and about how she'd like that to happen. Her plan does not involve being dumped by her district's voters in a low-turnout summer primary.

"When I decide I'm not running, I will announce it way in advance. There are a whole bunch of people who have said they are interested in running for my seat. We'll have a very open competition among those people," she said. "I think that open competition in the district will be better than anointing someone who wants to take me on."

But as Kahn knows well, no politician — not even one who has won 22 general elections — is in control of his or her career. The voters are. Further, elections are not anointments. The fact that the District 60A primary race pits newbies against an incumbent, and will occur on a date in which not many Minnesotans have a habit of trooping to the polls, does not detract from its democratic legitimacy or potential to end a career.

When Kahn forsook the research lab for the Legislature in 1972, she entered a realm in which one is up for "tenure review" every two years and in which experience is not always valued. Kahn has a long list of legislative credits that include the pioneering Clean Indoor Air Act, a gender equity rule in public school athletics, and a host of bills banning discrimination, protecting the environment and using technology to make government services more efficient. But those achievements may or may not impress her "tenure review board" on Aug. 9.

As she spends another summer knocking on doors, Kahn must be heartened by the nation's willingness to entrust high elective offices to politicians eligible for Medicare. As the baby boomers reach their 70s, they are redefining old age — for the better, I'll claim. Age-based stereotypes persist, but they are eroding rapidly in the face of ample evidence of the capabilities and contributions of people who are both seniors and citizens.

Yet Kahn must also recall the words of the late Senate Majority Leader Nicholas Coleman, who took the Senate's reins just as she arrived in the House, and whose cancer-shortened life inspired the public service of his son, St. Paul's three-term Mayor Chris Coleman. The elder Coleman instructed rookie legislators and reporters, "The most effective political slogan in Minnesota is 'Time for a change.' "