Most people in the US have three rounds of active disease for 8-10 years. If it is longer than that, severe, and they go into remission, it typically does not return.
The things that have killed the majority of my friends with Behcets are side effects and conditions from treatment(s) they received, a lack of accessible medical care, and/or medical malpractice.
Having a good team of educated Physicians who you trust is imperative. Your life may depend upon it.
For me personally, I started having symptoms at 5. It got worse until I was 9 when I was clinically diagnosable. I was pretty stable at that level with medication until I was 27 when I went into remission. Then, I got pregnant because my doctors said now or never. I'm 44. I've been so sick since that I long for the kind of sick I was before.
Everyone is different.