I think it’s a common misconception for admins/other roleplayers to think that older faces don’t ever get taken. It all just depends on what roleplays you are looking at- for example, RPs such as Valley of the Damned, The Compound, The Great Race, and The City have older faces that are taken. In my opinion, it depends on what kind of roleplay you’re looking at, and more specifically, WHERE you’re looking. It’s getting harder and harder to find a roleplay not centered around teens in the roleplay tags.
I think that you should definitely go with your idea, promote properly, and stick to it, and you’ll get your characters taken.