D.O.
For what it's worth, I've hated milk ever since I could remember. And I'm not even lactose intolerant. My mom said the minute I started solids I refused all milk. Throughout childhood she tried everything to get me to drink milk -- bribes, threats, etc -- but I wouldn't budge. Even now as an adult I won't drink it. I tried after I had my kids but it would make me gag and literally throw up. But I love cheese & ice cream & many other dairy things.
So what I'm saying is, it could just be a personal taste thing. From my own experience, I would advise against forcing him. It would become a major power struggle that I think you could do without.