Tell your dad to f**k the hell off. Seriously. Tell him he's an old man and that he isn't a car expert. That is, unless if he actually knows things, which is unlikely based on his response.
When I first got my car, my stupid 'know it all' dad goes oh yeah, it's gonna have no power until you get the turbo 'cooking'. He goes, nah, it'll be slow too. Taking him for a spin aroudn the block shut his uneducated mouth up quick smart.
Secondly, I normally shift at 2.5k rpm around town. Driving fast in small streets is just stupid.
When doing mountain passes/trackwork, I shift at any rpm, whatever iis required and i'm not scared to rev it.