This does partially fall into the 20 year rule, but it's also hard to say because "Moe" is a fairly general term.

Could you expand on what you're talking about? 'Moe' can refer to anything from "obnoxiously cute" to physically-attractive-but-tragic type characters.

In theory you could, arguably, trace the character archetype of one all the way back to the 11th century with the writing of Tale of Genji, while the other is a divisive term with purely modern connotations.