The inhabitants used to fall victim to cullings by the Wraith, like most other races in Pegasus. However, around five hundred years ago, an Electromagnetic field generator was constructed, as a means of defense against the Wraith, meaning the inhabitants were possibly once a technologically advanced race. However, the protection only had a limited area, so to control the population, they formed a ritual to terminate one's life on the eve of their 25th birthdays, meaning the eldest member would be no more than 24 years of age. The electromagnetic field generator fell out of knowledge, and the inhabitants believed that the Wraith cullings no longer occurred because the sacrifice ritual kept their population young and undesirable to the Wraith. From this belief also stemmed the idea that if anyone older was to stay for a prolonged period of time, the Wraith would again attack.
At around 2004, the First Atlantis Reconnaissance Team encountered the inhabitants, and learned of their culture. They managed to have convinced the people the truth of their suicide ritual, and stopped them in doing so. Dr. Rodney McKay found out the generator was powered by a Zero Point Module, and intended to use it to power Atlantis' shield, before learning the fact that it was nearly depleted. He was forced to bring it back and was able to tweak the generator in such way, that the field would expand the protection area as such, that it wouldn't drain as much power from the ZPM. The field would also allow them to grow their population. (SGA: "Childhood's End")