How old is old enough for candles and incense in their room?

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I have a 13 year old sister-in-law who is intelligent, responsible and has good common sense. The problem is that her mother's boyfriend :P says she's too young to have candles and such in her room. I was way younger when I was allowed to have those in my room as was my sister. I feel like he's being unreasonable, he has a lot of problems and is the type to say no just to make someone mad. She uses them when she stays at our house which is very often with no problems. She has no history of causing an problems with then either. His kids however are all drug addicts and ex cons (7 of them!) and of course usually end up setting things on fire and forgetting things are burning. It's frustrating because it's such a small thing really and I know it's kind of petty but I was wondering if maybe she is too young and my own experience has made me biased in some way. What do you think?