First, anyone can be a Witch, if they are willing to work at it. Age doesn't matter.
The reason we use unscented candles is because scent is a powerful part of magick, just as color is. People learned a long time ago that certain scents conjured thoughts, ideas, and images in their minds. When you use unscented candles, you can use herbs and oils to give those candles the exact scent you need for your purpose. If you can find a scented candle that has the fragrance you need, you can certainly use it.
I don't know what you mean by "charm necklace oil", so I can't really answer your question.
