Regarding the graph showing rates for over 80s and under 80s falling the same, this could just be coincidence.
The over 80s are generally less mobile than the under 80s - many in homes or housebound; a far smaller proportion of them go regularly to the shops, use buses, trains, etc. even in normal times. I doubt many will have changed their 'lifestyle' significantly over the past month, and yet we see a substantial drop in cases for this age group.
On the other hand, the under 80s have been in a forced lockdown. Like many I have stopped seeing family both indoors and outdoors; I haven't seen my regular group of friends outdoors since that was banned late last year; lots of children are not in school; a lot of shops are closed; my OH does the shopping without me or vice versa. We walk most places rather than taking the bus or underground.
So unlike the over 80s, many many under80s have been forced to changed their behaviour significantly and in doing so now have contact with far fewer people - yet both graphs show a substantial fall.
I still have my fingers crossed that the drop for the over 80s is the beginnings of the vaccine effect whilst the drop in the under 80s is the lockdown effect.