I think ageing it up is a good idea.
I agree that there's nothing iconic about Nano's character design. So my suggestion, alongside Hff's ageing up of the character, is to add a few references in the form of pins, badges, stripes, hair clips and so forth, that more experienced chatters will recognize. I think it would be a good way to get a more distinctive character look without feeling cluttered and overdesigned like so many vtubers feel.