Im 6ft 3 myself, I think 10% bodyfat is achievable for me. I had 4% at age 16 but was very skinny and a basketball player!
The most accurate test for BF is called Hydrodensitometry and it's most frequently used for athletes, other than that calipers if used by someone that knows what they are doing are reasonably accurate , however throwing around that number I doubt you had either test . The most elite professional bodybuilders are able to achieve the lowest bodyfat known which is around 3%, this is attainable for a very few of them and can only be maintained for a matter of hours and as is well documented can often result in death .
The most accurate test for BF is called Hydrodensitometry and it's most frequently used for athletes, other than that calipers if used by someone that knows what they are doing are reasonably accurate , however throwing around that number I doubt you had either test . The most elite professional bodybuilders are able to achieve the lowest bodyfat known which is around 3%, this is attainable for a very few of them and can only be maintained for a matter of hours and as is well documented can often result in death .