If you are 14 years old and you weight 70 kg does that mean that you are obest?

Based on averages then 112.0 lb (50.8 kg) 64.5 inch (5 foot 4 and a half) (163.8 cm)

Based on 5'2 then you are over expected weight by 20 kg. However, this is a guide and does not take in to account the actual physical shape of the person and their interaction with sports/physical activities. This can increase body weight and the weight might be more muscle mass. Also during the pubescent stages weight can fluctuate considerably as the male is still growing at this time