CasesByAge
(This graph should auto-update daily at around 4.30pm UK time. You may need to hit shift-reload or some such to defeat your browser's cache.)
Update on 11 December 2021: Age bands changed so we can more easily see what is happening with young adults where there has been recent steep growth.
The idea of this graph is to attempt to make use of the most recent information from public data about the number of confirmed cases in various age bands, so that trends over the last few days can hopefully be discerned. The numbers in each age band are adjusted/corrected for their incompleteness, then corrected for day-of-week biases, in both cases, as far as possible, in a non-laggy way.
These graphs are a reflection of the number of confirmed cases. It is possible that confirmed cases can increase without infections increasing if a greater proportion of infections are detected, and conversely it is possible that confirmed cases can decrease without infections decreasing if a lesser proportion of infections are detected.
Note that, as a consequence of the last few days' information being incomplete, the case number estimate for these days can sometimes be retrospectively updated over the next day or two.
Program: https://github.com/alex1770/Covid-19/blob/master/casesbyage.py