I'm 52 yrs old+ my dentist found. A split in the roof of my mouth...Does this mean I need surgery? What causes this?

It depends. It depends on where the split is and what it looks like. There is a huge range of possibilities including normal undulations of the roof, holes that lead to the sinus, and cancers. I recommend you see your doctor to get this checked out.
Is it in the gum. Is it in the gum or through the bone too. This could be a variation of normal anatomy --or not. What does your dentist say?
Probably not. You were probably born with that split and it is not severe and has always been there. If it is not causing you any problems or discomfort it should not cause you any problems in the future. Depending on where it is, unless you need dentures, i can't imagine why you would need surgery.