The Department of Agriculture is beginning work on its 2012 census, and Merrigan is afraid the average age will be even higher when the data are compiled.
"If we do not repopulate our working lands, I don't know where to begin to talk about the woes," she told the Associated Press in a phone interview. "There is a challenge here, a challenge that has a corresponding opportunity."
Merrigan, a former college professor, is making stops at universities around the country in hopes of encouraging more students to think about agricultural careers. She was in New Mexico and Arizona recently, and had stops planned last week at the University of Colorado in Denver and Michigan State University.
Aside from trying to stem the graying of America's farmers and ranchers, her mission is fueled by a recent blog posting that put agriculture No. 1 on a list of "useless" college degrees. Top federal agriculture officials are talking about the posting, and it has the attention of agricultural organizations across the country.
"There couldn't be anything that's more outrageously incorrect," Merrigan said. "We know that we're not graduating enough qualified aggies to fill the jobs that are out there in American agriculture."
Add to that a growing world population that some experts predict will require 70 percent more food production by 2050, she said.
Matt Rush, director of the New Mexico Farm and Livestock Bureau, was in California last weekend speaking at a conference for young farmers and ranchers. He made the same point.
"I truly believe we're at a golden age of agriculture. Global demand is at an all-time record high and global supplies are at all-time record lows," Rush said. "Production costs are going to be valuable enough that younger people are going to have the opportunity to be involved in agriculture."
The aging trend has been decades in the making. Between 2002 and 2007 alone, the number of farmers over 65 grew nearly 22 percent.
New Mexico tops the list of states with the highest percentage of older farmers and ranchers at 37 percent, followed by Arizona, Texas, Mississippi, and Oklahoma.
For every one farmer and rancher under 25, there are five who are 75 or older, according to Agriculture Department statistics.
While Merrigan can't explain why New Mexico is leading, she said the challenges for young people entering the industry are common across the nation - from escalating farmland values to accessing capital.
USDA has programs aimed at developing more farmers and ranchers and at boosting interest in locally grown food. In 2009 and 2010, projects in 40 states helped add thousands of new farmers and ranchers to the ranks, Merrigan said.
The National Young Farmers' Coalition has also been pushing for state and federal policy changes to make it easier for new farmers.
Rush and New Mexico farmer and rancher Pat Woods said it will take streamlining the system to make a difference.
"There are a lot of programs through USDA for young farmers and ranchers, but any of us know when you're dealing with federal programs, there's enough red tape to make the red tape blush," Rush said.
Woods started ranching in his 20s with help from his father. He's now 62 and is grooming his own son to take over the family operation.
"I'm trying to do my best with some kind of succession," he said.
"I'm putting my son in the hot seat. He needs to know how to make the day-to-day decisions on feeding the cattle and farming the land and making decisions on how to get the tractor fixed and all of that kind of stuff. I'll help him on anything he needs help with, but there's a lot of this stuff he needs to do on his own to learn."
Regardless of age, Woods said, farming and ranching require determination.
Ryan Best, 21, is determined. His mission is much like Merrigan's. As president of Future Farmers of America, he has been traveling the country, visiting with high school students about careers in agriculture. Best hopes his message - that this is a new time in agriculture - will resonate enough with the next generation to turn around the statistics.