How about baby/foal S1-design-having Luna, which is currently banned from being tagged with S1 Luna?
I’d prefer ‘S1 Luna’ to be aliased into a tag that means that design, without the needless tie-in with the season and exclusion of baby Luna… But that’s another discussion probably.
As for Celestia, I do agree, ‘pinklestia’ is originally the pink-bodied alt design.
Suggesting ‘pre-ethereal Celestia’ for any and all Celestia (young or mature) with the pink-maned ‘younger’ design.
Also suggesting ‘pre-ethereal Luna’ for any and all Luna with the S1 ‘younger’ design.
This would be a consistent way of naming these related phenomena and not require an age in the tag name. (I think most of the fandom agrees that becoming ethereal is something like a further ascension, tied not to age but to personal growth in wisdom and virtue. And what is ‘young’ to a near if not totally immortal character anyway?)