Warning: Spoilers for Star Trek: Insurrection.
The Ba’ku and the Son’a are encountered in Star Trek: Insurrection, and are presented as playable species below. (The Son’a were presented earlier as NPCs.) While the Son’a could have been encountered as early as 2371, the default time period for Star Trek Adventures, the Ba’ku should only be playable species after their encounter with the Enterprise-E in 2375.
The Ba’ku cast off all advanced technology, deciding to live an agrarian lifestyle on a planet with curious healing and youth-restoration properties. They are very long-lived. Some Ba’ku are able to slow time around them, and might be able to teach this to others, although only where there is a strong bond and if the learner has the mental fortitude to learn.
The Son’a were exiled by the Ba’ku for embracing technology and violence. The Son’a went on to conquer the Tarlac and the Ellora and made them indentured servants, but they found that without metaphasic radiation, they are aging and soon will die. They sought out different ways to extend their life, but that could only sustain them for so long. They also sided with the Dominion during the Dominion War, producing tetracel-white. In 2375, they teamed up with the Federation to relocate the Ba’ku so that they can harness the unique metaphasic radiation in the planet’s rings, and uncover the secret of eternal youth.
It is only through the intervention of the Enterprise-E that they discovered that the Ba’ku and the Son’a are in fact the same species. That secret is only revealed in 2375, but thereafter, the Ba’ku and the Son’a reconciliated, so it’s possible that ‘good’ Son’a can come to the fore thereafter. Likely, the lifespans of the Son’a would be restored to some extent by spending time on their home planet, but it is unknown if their deterioration can be completely reversed.
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