Seriously it's a tough one and a very interesting topic I'd say because it's like putting our skills to a test. When I mean skills, I mean how well you can make guide and train someone in the digital world and not just being an investor.
Before I'd start, I'd put into much consideration the fact that you're from the seventies which had limited or no technology as compared to the modern day in order for me not to keep my vocabulary in check in a way that I'd not end up confusing you with my words because according to you, you have not knowledge about Bitcoin.

The first thing I'd want you to know is you investing something or an amount you can lose because the concept we're talking about isn't one that is fixed. I'll use the price of Fuel for example to make you understand how it works. Using how the price of petrol goes up and down and if you are a seller who bought it in large quantity when the price was up, you'll definitely suffer loss if something happens and the price goes down. I think as an elderly person with wisdom, such illustration will help to give you the knowledge on how the price of bitcoin works so if you want to invest, you'll definitely be expecting the possibility of loss as that of profit.

Another advice I'd give you is to have the element of patience. Bitcoin is a tendency that is not rushed because once you do, you'll never gain from it. You can purchase it, keep it there in your wallet since it can be monitored by you having no third party involved. Allow it to go through the waves of time because there might come a day the price will drop but that's definitely not the end of it and that's why it's called an investment. Now in Bitcoin's case, it's not just any investment but a long term investment which may pay off in even a year or more than. So before you should venture into Bitcoin investment, I'd really really lay concrete and lengthy emphasis on the need to have patience because I know you been an elderly, you'll be much aware that patience as we know it, is a virtue.