Which is probably why SE have been putting them (Lalafells) in positions that you'd normally see adults in. Political leaders, accountants, etc. Lalafells were also created by Tanaka's team because of the Tarutaru in FFXI; as an attempt to get people playing FFXI to easily transition to FFXIV 1.0 (familiar races and all that). The Tarutaru also actually had children, which were actually smaller than the adults (I feel FFXIV should have done the same and not make the supposed children NPC's look exactly the same as the adults).

SE also already have a "forever young" race: the Padjal. They'll never be playable due to lore reasons, though and yes, the lore for them is actually more restrictive than the one for Viera. Padjal are only 'born' from a very specific/rare bloodline/family, if memory serves. Elementals don't just pick a rando peasant kid and go "you kid forever now lmao."