It appears average height is around 5'9", and average weight is around 180lbs... but it completely varies by geography and ethnicity. You can check out my related link for a good source on average...
Please note that these are the AVERAGE heights, not the height your child has to be to be growing healthily Boys 12 years old - 4'9 to 5'0 13 years old - 4'11 to 5'3 14 years old - 5'1 to 5'6 15...