My dad is 6'6 my grampa is 6'7 will i continue to grow until the age 25 because im only 6'4 and i'm 18?

Growth: Your adult height is determined by when your growth plates close, which varies from person to person and from bone to bone. You may gain a little more height, if your growth plates are not closed/fused yet. If they are, then 6'4" will be your adult height. Also take into consideration height on your mother's side as well, that can contribute to your final height.