Ok, i have a question about walkin,?

ok, i am 13 years old, 5'7" 159 pounds. I am on a diet, and my goal is 130. is this a good goal? OK now to the real question, if i walk an hour every day and eat around 1000 cal. a day, do u think i can wear a 2 peice swim suit by next summer around this tyme? plz im so desperate! am i EXTREMELY fat? idk....i don't know how much i am suppose to weigh