In the early days palm scripts and writings on metals were used as a source to secure data in my country. These scripts can't be read by everyone, and these data will be piled up as a booklet. We can explain the present days blockchain technology relating to the old way of data saving. Surely old people will be aware of these scripts and for the reference I've added few images of the palm scripts and writings on metals.

Sending and receiving Bitcoin through QR code may be the best way for them as they don't have to manually input and check addresses which are oftentimes in small fonts.

The fundamentals of Bitcoin should be enough for them. Security in general, dos and donts, and some tips on how not to get hacked or phished or scammed are also very important for them to understand.

Also, their wallets should only contain amounts that they could spend on a daily or weekly basis. I guess regular refills could be done by their children or grandchildren who are more knowledgeable about Bitcoin.

they don't need to understand bitcoin to use it. in fact that goes for a lot of things. for example how many people (not just elderly) understand how credit cards work? but they use them all the same. all anybody needs to know is that bitcoin is a new form of money that is highly secure and still has a volatile value. anything more than that is optional and is needed for anybody who is interested in the technology or wants to look under the hood.

Im not sure that they really need/want to understand bitcoin. If they dont want to use bitcoin then just accept this

Hi,
OP:
It is simple do not teach her! (1)

I can tell you that in my environment, all the adult people I know do not like to call them "oldest old," but they handle social networks better than I do.

How did they arrive! Out of curiosity, my grandmother who is 75 years old currently started using the popular messaging system in 2011-2012 I remember it well because I was the one who downloaded the apps. That is to say, she was 68 years old, she was already quite old, but within the limits of calling her an old man, for my old man she is older than 75 years.
 
At first she was ignorant of it, but what interested her were the groups in the Apps, that was all. But she'd been ignoring her, she wasn't interested.

With the bitcoin issue, I take advantage of the fact that he likes whatsapp and I send him news, memes and fun things related to bitcoin. There is good documentation about bitcoin without going into technical details.

Anyway, do not try to teach an old man something that he does not ask, the "old man" who wants to learn or does it alone, or asks for it, friend, they are older people who have lived, they are the experience of life. But, that if! creating curiosity is the best way.

(1) Please, this is a charismatic comment, which seeks the interpretation of my post.

Finally,  each older person is different, I think it is in each one to understand these wonderful people.

It's a bad idea teaching old people to use bitcoin. Mostly old people in my country don't know how to use cellphone or computer. But if they knew, what will be in their mind if you introduce bitcoin to them? In news, bitcoin always mention because in our country many investment scam use bitcoin as their mode of payment. Old people always watch news, and if I'll introduce it to them they'll avoid it and think that it is a scam.

They don't need to know about the "bitcoin revolution", the technology behind it or any technological knowledge. Those knowledge would be absurd for them.
Instead you can just teach them how to send, receive and keep your wallets secure. I don't think any wallet have any kind of accessibility features. But if accessibility is still an issue, as far as I am aware, all operating system comes with accessibility feature which can be used with your browser or any application on your computer.

It would be difficult to teach the specifics of bitcoin or cryptocurrency to the elderly since most of them are not well versed in technology. They just need to learn the concept, how it works, how to secure, spend, and transact. People easily adjust to things that are massively used, the same as how we learned how to use the internet. Not all of us are into tech, but as it becomes a part of our daily lives it will be easily absorbed and adopted.

I think it is not a bad idea.

It is just that most of these old people are a fan of the government, telling them that something like a Bitcoin that is centralized and not controlled by the government could raise suspicions to them telling you their theories and even ludicrous claims against Bitcoin and cryptocurrencies. I kind of experienced it so I immediately stopped. Some might find them interesting but most of them would just don't care and may find it suspicious.

I don't see any strategies that will work in teaching the old about Bitcoin.

We know already that the old people doesn't have the capability to memorize things because of their age, their are tend to forget easier compare to those people who are around the 30's or 40's. It is hard for them to teach Bitcoin especially for those old people who are not techy or not even exposed to the technology since on their prime, things like this doesn't exist at all. There are some old people too that will just ignore it since they are old already. They don't have any time or at least interest to learn it.

In my place, I'm the only one who knows the basic things of crypto and I'm not teaching it to any of them. Its not that I don't like but I don't feel that they are interested on it too.