Which one of the following two sentences is correct/proper?
My grandpa died 30 years ago. I have never met him.
My grandpa died 30 years ago. I never met him.
Well, we only use "meet" for interacting with people who are alive. So if you never met your grandpa, you would say it like that: with never met.
The simple past (met) excludes present and future time. So, the simple past refers to an action that is completed in the past. When you say never met, it means in no time in the past did you meet him. You can say this whether you are 20 or 40, that is, whether you actually had the chance to meet him or not.
When you say have never met him, you are actually talking about your present situation. And the present perfect would imply that you still have the opportunity to meet him. But this is not true, since he died 30 years ago.
Now, for a bonus, let me throw in this. If, in the past, you did have a chance to meet him (that is, you were old enough to meet him when he was alive, but you did not meet him), then you can say
I had never met him.
The past perfect talks about a specific moment in the past. Here the specific moment is your grandpa's death. So,
He died 30 years ago. I had never met him (before he died).