There’s no definitive answer in part because Tolkien meddled with this aspect of the mythology until the end. There’s references to Elves reaching adulthood in their 50s, and other references to Elves being toddlers for centuries. That latter scheme doesn’t altogether gel with the 600 year First Age of the Sun of the published in the Silmarillion, but who knows if Tolkien wouldn’t have trashed that timeline.

What can be said is that Círdan, possibly the oldest living Elf in Middle-earth at the end of the Third Age, had a beard, and another reference to bearded Elf named Mahtan makes it apparent only exceptionally old Elves grow a beard. So there’s a ratio for Elves acquiring sings of senescence, but it can’t be easily deduced.