See, to me, that looks like an intolerable imposition onto my basic humanity. It's legal for me to remember you, but not to write down anything about you in my diary? Does that not seem unsound to you? Does it not seem to trample all over common decency and common sense, to in some way cause harm to older people who can't just rely on their grey matter?

I freely admit that keeping a diary is not the same as keeping customer details, but that's the point here: why are they treated the same?

There is a qualitative difference between degrees of data collection. What you can see and remember is a different category from what you can write down; what you can write down is a different category from recorded audio/video; what you can record with conventional equipment is a different category from what you may capture and store using all available technology e.g. DNA sequencing. In general, the more powerful the technological aid, the stronger the regulation.

Even just the first two, seeing and writing down, are legally distinct. Supermarket checkout staff handle hundreds of credit cards a day. How do you think the law would react to such an employee writing all of them down?

It's not discriminatory against old people, because even a completely amnesiac person armed with a notepad can permanently capture vastly more information than all but a photographic memory.