Level Limits - Defined by the Story

I was searching through old posts today, looking up what now seem like ancient and long-forgotten details about an event that took place twelve years ago in my play-by-post campaign and stumbled across an article about level limits in AD&D. This concept has largely been abandoned over the intervening decades since the creation of Dungeons & Dragons with 5e essentially capping out at 20th level for everyone but it got me to thinking about the story my players are currently engaged in. In earlier editions of the game, it was commonly accepted that the time of elves and dwarves, et al has passed with them reaching their "maximum potential" somewhere between 8th and 11th level. Humanity is the mover and shaker of the world now but it seems to me, and always has, that an elf with a lifespan of hundreds of years is going to amass more experience and have more time to hone his skills than any human. The same can be said for dwarves and gnomes who also can expect to live to...