need help on board buying

hey, im 14 years old and this is my first board that i am actually buying or making but my first board i bought at a tag sale. it is a 6’0" board 3 inches thick but just a regular short board. theres the history. now i want to get a new board but i dont know dimensions. thats where you come in. i want about a 5’8 5’9 fish. but i dont know any other #s. so i weigh 135 and am 5’6" tall and am still growing. i want this board to be a board i use for at least 5 years so by the time i get a new one ill be a lot bigger. any suggestions on the dimensions???