My height is 5'6" .my father's height is 5'5".i attained puberty at an age of12.what could my height be if i had reached puberty at a later age?

Well, you are now: 21, so no matter what you have reached your maximum height.

Hard to say: Both parents have an equal input into your height potential.The final height,timing & duration of puberty is genetic & the parents provide the genes. Puberty is also a transition period, so you could start at 12 and finish at 15 or 19 with a different in final height. You have what you were endowed with.Accept it & move on with your life.You could have been a lot shorter.