Transport for London (TfL) regularly publishes demographic details of taxi and private hire drivers here: http://content.tfl.gov.uk/taxi-and-phv-demographic-stats.pdf.

It is not possible to predict the future demographic changes in the taxi or private hire trades with any certainty, although just as in every facet of London life we would like them to reflect the communities they serve.

Please see my response Mayor's Question 2019/6172 which provides more information on the work TfL is doing to promote the Knowledge of London as an attractive career option.