When were the photos taken? Are they recent or from earlier in the year (I notice you have been posting other photos from January/February)? That may help to resolve the age.
In my experience, juvenile sunbirds usually show a fairly obvious pale gape line and pale base to the bill. Although this would become less obvious over time, I don't think your bird is a juvenile (at least not a very young bird). Personally I would say that this is a female Fork-tailed Sunbird, most likely an adult.
