Dear patient At 17 years of age tibia fibula fracture takes 8 to 12 weeks to unite normally but there are many variables 1. Fracture type like simple 2 part or communition 2. Type of reduction and stability achieved by surgery 3. Simple or compound fracture 3. Smoking and alcohol habit etc. So you need to regular follow up with your operating surgeon monthly and xrays every monthly. Weight bearing can be started once Xray is showing signs of fracture union. Do not take any chances and take regular visits to your operating surgeon and do what he says as he knows your condition best.