Perfect from a health standpoint are 12 %. Under 10 % is already not healthy, but as been said before, highly individual.
Even BB in contest shape have mostly around 10 % BF. The "trick" of the BB is that they only use the caliper to measure their BF, but the caliper only considers the subcutaneous fat and not the visceral fat. So when they claim 3-4 % BF that's bullshit, that's only the subcutaneous fat.