Advise please: Violin lesson for boys

My boy is five now. And we are thinking about starting his violin lesson.
I would prefer him learning piano first,but he doen't want to. He wants to start violin (because, he said, it is harder). I am hesitate because practice would be a big headach for me. (he is kind of strong minded kid, hard to convince him). My questions are:
1)What is the proper age to start? By that I mean the older starting age when kids still have a very good chance to achieve high level.
2) Suzuki vs one to one lesson, which is better?

Thanks.