Humans form individual memories at 2-3 years. Elves don't start forming memories of their current lives until 30+ and this is considered a tragic event in elvish culture as it generally marks a close on remembering Arvandor. The about 100 year mark is termed the closing of the veil as the lose the ability to remember their former lives.

You term it as a goal post, but they view it as a cutoff. It's more the spigot has run dry than they want to venture.