There are numerous high quality gyms in all different shapes and sizes. 

http://thecenterforfitness.com/ The Center for Fitness is a big gym with Weights, Yoga, Aquatics and aerobics. It is focused more on the seniors but there are members of all ages. They have been in Kerrville for over 40 years. 

http://www.kerrvillepeak.com/ Peak Fitness has a large facility also with cross fit, weights, various classes and personal trainers. Age groups are all over the map.

http://kerrvillekroc.org/ The Kroc  Center is huge and has a lot more seniors than some of the other gyms. Beautiful facility.

https://www.goodlifefitnesscenter.com/ New and high tech. Small but lots of neat equipment. Younger crowd. Even have cryotherapy.

https://www.anytimefitness.com/gyms/3234/Kerrville-TX-78028/?utm_source=bing&utm_medium=local&utm_campaign=localmaps&utm_content=3234 Newer 24 hours fitness. Small but plenty of equipment for fitness enthusiasts. Younger crowd.