hi i agree in total with alophysio. If a screw will implanted the fracture should be stable, but concerning to the history of that young guy you should be careful with weight bearing. water gymnastics and under water jogging seems to be an option for CV fitness. also all other strenghtening of quats, hams gluts etc. is ok. also keep flexibility of muscle around ankle knee and hip joint. usually a fracture needs about 6 weeks to be stable enough for full weight bearing, but talk to the orthop.
and keep this guy motivated!!!
cheers