Difference in male vs female use of the English language
Yes, this is possible. Deitrick et. al. (1) describes a model that yields 95% accuracy in classifying the gender of the person based on the e-mail that he/she wrote. Apparently men and women tend to have differing word choices. This research is based on the Enron corpus, and thus meets your criteria of non-professional writers (all of them were Enron employees, hence the percentage of journalists or fiction writers would probably be small).
- Author Gender Prediction in an Email Stream Using Neural Networks, 2012
I don't know how accurate they have got but there are ways of telling the gender of a writer based on word usage - at least for fiction.
The famous author V S Naipaul claimed that he could easily tell based on women's more emotive language - there is a test based on his claim in the Gruniad (UK newspaper)
There is a website based on some CS research that uses word choices to guess