I have explained bitcoin to many people, old or young doesn't matter they are the same. some might understand it easily and some might not. what i do is i just tell them the basic and then i give him some link to an article or video that explain Bitcoin or Cryptocurrency and the technology. if they really want to learn it and have something that they don't understand they will ask you some questions.
How would you explain to old people how transaction cost is calculated? With banks, it is more or less clear to them that transaction fee is a constant, no matter what amount you are sending. Or it might change if the transaction is to abroad bank that does not have friendly correspondent bank with their bank. Look, even this aspect is hard to understand for some old people. And I'm not saying that transaction fees are different if they make 5 or 1005 transactions per month (just an example).
But how would you explain to them about imputs, outputs, the size of your transaction, mempool and the fact that a change address might appear in their transaction chain.