You can be an artist at any age, but I don't think that's really what you're asking. Most people asking this question are really asking, "Do I have any real shot of 'making it' if I still haven't 'made it' by a certain age?" The answer to that depends on what you believe "making it" is. There is truly an audience/market for everything, but you have to know what yours is that you're going for. But you have to have the self awareness to know whether or not what you are offering fits your desired audience/market. If yes, then yes, you can make it no matter how old/young you are. If not, then no, you won't make it no matter how young/old you are. Remember, we don't sell music, and we never have. We sell feelings, fantasy, and the occasional physical product. Our music is just the tool needed by tour audience to have those feelings, fantasies, and products. Are you the feeling and fantasy you are selling? Therein lies your answer.