The effects of auto-brewery syndrome
The gut microbiome is extremely complicated, and almost anything related to it is only partially known, therefore prone to oversimplification. Trying to explain the phenomenon of gut fermentation syndrome in such a limited fashion (age, gender, ethnicity, quantity of one particular yeast, etc.) will not help us understand it.


  Common yeasts (C. albicans, C. tropicalis and Torulopsis glabrata) and Saccharomyces cerevisiae are able to ferment sugars through the homolactic, heterolactic or mixed acid fermentation pathways, with ethanol as the major end product. 


Candida is a very common yeast found in the environment and in and on our bodies wherever it's warm and moist (therefore the GI tract.) Candida species are the most common cause of invasive fungal infections in humans (followed by Cryptococcus and Aspergillus) and can involve any organ. Yet it's omnipresence does not result in clinically recognized cases of ethanol intoxication in even a minute fraction of people who carry it in their gut. 

Case reports started appearing in the literature starting in 1972, yet it is still a rare event to see one. In 2001, the case of a 13 year old girl was published. She had short gut syndrome and became intoxicated after ingesting carbohydrates. She had been placed in a rehabilitation facility with no access to alcohol, but still had positive blood alcohols. Aspirates from her small intestines grew Candida glabrata and Saccharomyces cerevisiae. Short-gut syndrome is complicated.

We have no idea how common fermentation into alcohol is in the gut, or what the results are, but it is probably far more common than recognized, can probably result in effects other than intoxication (for example fatty liver disease in non-drinkers), and probably has a role in other illnesses.
It's complicated:


  Carbohydrate metabolism by gut microorganisms is a central process allowing supply of nutrients and energy to the host. This fermentative process is complex and involves several functional groups of bacteria with complementary metabolic activities that interact to ensure the biotransformation of polymers (resistant starch, nonstarch polysaccharides, proteins, mucins…) into end-products (mainly short chain fatty acids and gases). Hydrolytic communities transform complex substrates into smaller fragments that can also be used by other bacterial groups unable to hydrolyse polymers. Other microbial cross-feeding interactions are related to the utilisation of fermentative products such as succinate, lactate or hydrogen and involve specific groups of microorganisms.


All we know is that it happens in some people, and that it can respond to antifungal treatment and some probiotic supplementation. "Why" is still a mystery, and speculation only.

Gut fermentation syndrome
Invasive Fungal Pathogens: Current Epidemiological Trends
IwataK., “A Review of the Literature on Drunken Syndromes Due to Yeasts in the Gastrointestinal Tract,” University of Tokyo Press, Tokyo, 1972, 260-268. Not available online
Functional dysbiosis within the gut microbiota of patients with constipated-irritable bowel syndrome
Obesity and female gender increase breath ethanol concentration: potential implications for the pathogenesis of nonalcoholic steatohepatitis