Elves of Solstice
During the Crimson Conjunction, 35 years ago, every humanoid over the age of 75 in Solstice (and surrounding lands for thousands of miles) was killed by the Fiery Time of the Necrologer, and none could be restored to life through any means. While the loss of scholars and wise folks of society as a whole was devastating, some races were more seriously impacted than others.
Orcs and half orcs barely noticed. Humans lost only their most wizened and experienced, but most positions of authority remained filled (though many by those with less long-term experience than might be desired). Dwarven and gnomish societies were devastated, as most guild leaders, matriarchs, kings and great heroes dropped dead with no warning. This is still seen as a dark time by these races, who struggle to regain the lore and experience stolen from them.
Elven society simple ceased to exist.
No elven adult survived. The majority of the race was caught in the Spring Years, physically adult enough to care for themselves but still incapable of long-term thought and short on reasoning and empathy. Worse, for decades this continued, with the entire race essentially ruled by the elven equivalent of teenagers, driven by hormones and spur-of-the-moment decisions, in some cases backed by birthrights of vast wealth and eldritch power inherited from those who had known better than to use it.
More than half of all elven nations, guilds, and families imploded within a decade. Those that survived either did so through sheer wild abandon, or due to allies who felt compelled to honor centuries-old alliances and pacts. But even now, elves are still a race of younglings and the oldest of them would only know be considered the most junior of adults. Elves are eternal children, and have been for decades, and have embraced the clothes, jewelry, piercings, slang, and devil-may-care attitudes of teenagers in a nonstop party that threatens to drive other races crazy.