A 4km race which is 2.48 miles is a fairly short distance race. Me personally have only run 3 mile races and 5k's. I'm guessing your mile times are somewhere between 7 and 10 minutes, so anywhere between 19 and 25 minutes would be a good time for someone your age.
You are doing 4k cross country at 13? that is awesome.
same answer as above, anywhere from 15-20 minutes is great