A
6'6" person saying they were something other than tall as a kid is like a black
guy saying he was white until he turned
18. What else could you have been even if you tried?
People would know a
6'6" person was always tall for their age as a kid without them having to explain it, the same way they would know a 4'10" person was always
short for their age, even as a kid (unless they are one of those rare Guinness record books folks), so explaining it would be redundant.