It is going to depend on what weight you want to achieve. They are slow growing, so keeping them until they are older is not going to be a problem with the quality of the meat.
The problem with a smaller pig is that the bacon will not produce very big slices or quantity. I would be inclined to keep them growing to at least a year - fourteen months.
Tracey has a young male lined up for slaughter - perhaps she can comment.
Keep us posted. I don't think any of us has grown a pure Mangalitza to slaugher weight yet, so if you are the first to try it then please tell us how it tastes. There are some recipies on here to try, to perhaps you could give some a go?
Kate

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Glad to be here and enjoying it!