Read one doc said its highly unlikely to grow signif. taller @ 40. what then would cause that for the rare few who do? aren't our bones fused by then?

Correct: The growth plates of long bones in the body are closed well before the age of 40 , and do it is really not possible to grow through that mechanism at the age if 40. From a surgical perspective, if a person has a deformity that is "straightened out" this will result in an overall increased height of that oatient regardless of the age.

Hormones: Significant increase in height at 40 would be very rare and usually associated with excessive human growth hormone from a tumor or exogenous source. Would be more likely to see increase in height before 25.