Your parents asking him questions is good.
Your dad telling you that you shouldn’t date him is advice.
Advice is also good. Be like your parents, and ask questions.
Such as, “Why shouldn’t I date him?”
“Why (or how) is he too old for me?”
“How would I be on the road to evil?”
Why does your dad think you’re doing drugs, having unsafe sex with strangers (or anyone)?
If you want them to understand you’re not a child anymore, act like an adult. Challenge false assumptions you’re aware of.
Start with asking questions. Not liking him is one thing. It’s subjective. Having false assumptions about him, and you, is something else. Get to the bottom of the false assumptions and correct them.
Be on the road to discovery.