Under 5: 6.4 percent
5 to 9: 5.7 percent
10 to 14: 5.3 percent
15 to 24: 15.5 percent
25 to 34: 14.4 percent
35 to 44: 12.0 percent
45 to 54: 13.7 percent
55 to 64: 12.4 percent
65 to 74: 7.3 percent
75 to 84: 5.1 percent
85+: 2.2 percent
Source: 2010 U.S. census
Over the last 10 years, teenagers and 20-somethings became Chattanooga's single biggest demographic, but it's the huge growth in their parents' age group that has officials taking notice.
Based on demographic figures from the 2010 U.S. census, 15.5 percent of Chattanooga residents are between 15 and 24, and three out of 10 Chattanoogans are between 15 and 34.
But while the number of residents in the 55-to-64 age bracket was smaller than the youthful group, it grew by 46 percent in Chattanooga and 51 percent in Hamilton County between 2000 and 2010, the census shows.
Officials say the numbers back up what they've known for years - that there is a huge group of baby boomers nearing retirement age.
"It's just a big bubble approaching the bursting place," said Lucy Utt, community services supervisor with the Tennessee Commission on Aging and Disability.
Overall across the region, median ages increased, meaning there are more older people than there used to be.
The median age is the point at which half the population is older and half is younger. In Hamilton County, the median age went from 37.3 to 39.3, meaning half of county residents are looking at their 39th birthday in the rearview mirror.
Several counties in the region are even older. Polk, Bledsoe, Marion and Meigs counties all have median ages above 42.
In 2000 none of the counties in the tri-state region had a median age over 40, compared with nine out of 20 in 2010.
"It wouldn't be a bad idea to get in the drugstore business," joked Doug Bachtel, a demographics expert with the University of Georgia.
Bachtel said most counties in North Georgia, North Alabama and East Tennessee are older than the national median of 37.2 because the region has a lower percentage of minorities, which typically have younger populations.
Whitfield, Murray and Gordon counties, all of which have large Hispanic populations, had the youngest median ages in the region at 34, 36.2 and 36, respectively.
Bachtel said most counties and towns in the country aged a few years because of natural population trends.
But communities such as Ooltewah and Lakesite in Hamilton County and Kimball in Marion County all had their median ages jump by five years or more. Bachtel said the numbers probably come from new people moving to the area.
Without knowing much about those specific areas, he theorized that a large number of retirees moving to those areas could have skewed the numbers. Tennessee in recent years has promoted itself as a low-cost, low-tax retirement haven.
He also said he wasn't surprised to see the increasing youth population in Chattanooga.
"Retirees don't move to urban areas," said Bachtel. "They move to the mountains or the coast."
But beyond understanding the trends, Utt and other state officials are trying to prepare for a wave of older residents reaching retirement age and beyond.
Janet Lamb, elder rights supervisor for Utt's agency, said she is concerned about an "Alzheimer's and dementia tsunami." She said science is in a race to catch up.
"That's what scares me," Lamb said. "We're going to have to have research to know how to deal with these people."
And as medical costs continue to climb, Lamb and Utt said families and the state will have to find some way to pay for the care of people who live to be much older than previous generations. Of Tennessee's 1.3 million seniors, one third are low income and require extra state services.
"The needs of that population will be enormous," Utt said. "We don't know how we are going to meet all of these things. The solutions are out there, but they all require money."