DONTFORGET: The Unofficial Story Mode Novelisation Prologue

(+ a screenshot leak from time travel)

Apparently, Frisk has seen in-game height, which they share with Noel, but has no confirmed age, though they share it with Suzy.

On other hand, Harlow has confirmed age, but it's unknown what was their height in UT.

What's your opinion on age range?

Deltarune x Homestuck Classpect Theory

(November edit, even though it's a jokey detail)