You asked
I would like to request the following data or the closest available proxy: the average disposable income for individuals in the 25-40 year old age group in all wards in London.
We said
Unfortunately, we don't hold the information you have requested on the average disposable income for individuals in the 25-40 year old age group in all wards in London.
Table 7 in The effects of taxes and benefits on household income, disposable income estimate: 2019, provides estimate for disposable income in the UK by age band.
Income estimates for small areas, England and Wales: financial year ending 2018 presents average income estimates for middle-layer super output areas in England and Wales, including London, but no breakdown by age.
For any further help, please contact hie@ons.gov.uk.