I think I'm a little older than you are, so I did indeed react like your father did. I was very skeptical, but instead of asking others for proof, I just put something like $2 worth of bitcoin in, then a couple days later I transferred some back out. This was sufficient for me to know that everything was on the up and up. Ask your dad for $20 of his money for the test, then do the transfers, recording all the screenshots for him, and ultimately showing him the money back in his bank account. I think this will convince him it's not a scam. If that doesn't work, he's a lost cause.