There is one overarching reason Brian Schatz is the senior senator from Hawaii: his age.

Schatz is 41; his Democratic primary opponent, U.S. Rep. Colleen Hanabusa, is 63.

Schatz was picked by Gov. Neil Abercrombie because, as the governor says, "He’s young. He now has had the opportunity to enter the Senate at roughly the same age as Sen. (Dan) Inouye."

Simple actuarial tables suggest that Schatz would be able to serve longer in Congress than would Hanabusa. Abercrombie’s argument is that if seniority is the measure of political power, then Schatz would give Hawaii more clout than Hanabusa.

In December 2012, while appointing Schatz, Abercrombie said part of his decision was based on his desire to "rebuild our seniority in Washington."

A campaign memo for Schatz’s Washington campaign summed up the pitch for support by saying, "Schatz has the promise of serving many years in the U.S. Senate and accumulating all important seniority."

Earlier this week, the AARP debate televised on KHON-TV provided the perfect forum for the pair to hash out the age thing.

"Your mentor, Gov. Abercrombie, says I’m too old to be a United States senator," Hanabusa said to Schatz when she had a chance to question him.

"Age has become an issue in this campaign. Can you tell me how old is too old to be a U.S. senator?" she asked.

Hanabusa is asking the right question. Since his appointment, the No. 1 reason given for supporting Schatz, a relatively unknown former state House member and lieutenant governor, is that he is younger than Hanabusa and therefore will be in office gathering seniority.

That premise, Hanabusa points out, is based on Schatz repeatedly winning re-election. The winner of this year’s race fills out the last two years of Inouye’s term and will run again in 2016.

The Senate seat does not come with a no-cuts contract. For instance, a strong possible opponent could be U.S. Rep. Tulsi Gabbard, who already had said she wanted to take Inouye’s place before the Schatz appointment was made.

Because of Inouye’s longevity and political acumen, Hawaii has had an almost cargo-cult worship of the ability of our federal representatives to bestow federal grants, subsidies and projects on the islands.

In January, however, Schatz supporters were not saying legislative skill was what we needed. Abercrombie told The Washington Post that he appointed Schatz because, "Brian Schatz is 41. Colleen isn’t. She’s in her 60s."

In response, Hanabusa said Abercrombie’s argument was "offensive" and added that it was sexist to tie a woman’s age to productivity because many women are raising families and not in the workplace.

During this week’s debate, Schatz also tried to push away from the age issue.

"I don’t think age has any place in this discussion or this election," Schatz said, adding that he also didn’t like the language in the circulated campaign memo.

The seniority issue, however, lingers. How important is it to have your U.S. senator squirreled away for decades and decades in Washington?

Apparently, not as much as it used to be. There is much more churn in the Senate. For instance, Schatz is ranked 84th in seniority because he was sworn in on Dec. 27, 2012. Mazie Hirono was sworn into the Senate on Jan. 3, 2013, and she is ranked 90th.

So the argument can be made that a Sen. Hanabusa would also rise quickly in seniority.

According to Roll Call, seniority for senators is determined by length of service and former positions held (Senate, vice president, House, Cabinet member, governor).

In the case of a tie, state population determines the order. In a case where two senators from the same state have terms beginning on the same day, seniority is determined alphabetically.

Hanabusa continues to argue that there is more to working with the alpha males in the Senate than age.

"That had nothing to do with seniority; this has to do with earning respect," she said.

The question of age is inescapable, but voters will decide if it tips the election to Hanabusa or Schatz.

Richard Borreca writes on politics on Sundays, Tuesdays and Fridays. Reach him at rborreca@staradvertiser.com.