you're working and earning something, that shows you can give them a reason to believe what you told them about Crypto,
I'm sure he needs more time to do that. It wouldn't make sense to say anything if he just started his journey, he can only prove a point in front of his parents if his investments start to earn him money because only that will make them believe Bitcoin and cryptocurrencies aren't scams but they are an industry where one can invest and earn money if they know what they are doing.
You're right because some parents only believe in show working that's to say try to believe when they see the positive impact of what you're saying but if he tells them about it when he's just starting they might still say some discouraging words to him. Some parents can only agree with you just to let you go ahead with whatever you feel like doing after every explanation and evidence that Bitcoin isn't a scam, it goes two ways. Convincing parents on such a thing is very difficult and you sometimes wish you never told them.
Parents will never discourage their children, so they were probably not trying to do that but they tend to get concerned and if they have traditional beliefs, it will take time for them to understand what these new things mean and how they work because they have never heard or seen of anything such as Bitcoin in their entire lives before.
Some parents won't mind discouraging their children not to do it just because they don't want to know about it and they would like the children to do what they as a parents want, is them trying to control every aspect of the child's life. Fine some might want the child not to fall into the wrong hands, that's the protective ones and some of these parents do listen but they try to be mindful of what their children are getting into. In some situation the parents can even support the child with little funds to start up his investment on Bitcoin because when it goes well for the child he'll be happy to share the good news that's if he learns from a better hand who have more experience in the crypto world.