If they need to reach adulthood at the same rate biologically so that they can defend themselves in the wild, why would a 100 yo elf ever be level 1?
It sounds much weirder to consider that elves and dwarves keep acting like teenagers 30 to 80 years past their human-like rate of physical maturity. Or don't they? What does adulthood even mean for them? Sometimes it sounds like they have a higher standard for maturity than humans, wouldn't also be some form of neurological development? But I never seen that manifesting in any practical way.
D&D worldbuilding is made a little awkward by how fantasy races age and develop drastically differently, but they also must become strong at the same pace, such that a 100yo elf can be completely inexperienced and grow at the same pace as a human during a week of adventuring. They try to have it both ways, but the more it's explained, the more confusing it gets.