Hi. You want to grow to 6'8" ?!!! But why ? Our growth in terms of height is governed by multiple factors and most importantly genetic factors. I feel it's a little late to take growth hormone and will be associated with some side effects. Limb lengthening operation usually require several months of care and wearing of casts. I definitely feel this may not be all the worth but if u are really bent upon the same, see a qualified orthopaedician . Dr Govind Suresh Mittal.