Currently I can determine keywords and concepts of a given text using the Alchemy API. But I'm also interested in the analysis of the text's targeted audience. Specifically, I'd like to know whether the text was targeting male or female audiences; or which age groups were being targeted. Is there a service that can support this type of analysis?
You could try using the Personality Insights API which analyses personality traits detected in the text. There is also a Tone Analyzer which will provide you with tones, social propensities and language styles from the text.
If you have a training set available (a number of example texts and whether the gender they are targeted at) you could feed these in to the Natural Language Classifier which will apply machine learning and then classify any new texts based on the learning from the training set.
I suspect that to get the most accurate results you'll want to use a combination of the above and manually build some algorithms to weight the results coming from each API.