I broke my hip when I was 36 (12 years ago).
mine was a femoral neck fracture;
I was advised by a GP friend to have a bone density scan for the same reason you have been - I was too young for that type of injury.
Result was that I had the bone density of a 75 year old man. I was advised to do two things;
1) take calcium (with whatever it is that helps absorbtion Vit D? Iron?) supplements
2) do some impact exercise (obviously post being weight bearing on the leg again).
I managed to return my density to age normal after 2 years and I've had bigger offs since with no significant bone damage so it's clearly had some benefit.
I also saw an endocrinologist (sp?) who did hormone tests etc but these were in the normal range (low testosterone can cause density issues).
If the exercise etc hadn;t worked they'd have moved to some sort of drug treatment I think.
For the immediate future I'd recommend;
1) gettign physio asap.
2) not let them treat you like a 70 year old where just 'gettign mobile' is the goal.
3) get a full set of stretches - gettign full movement back in your leg is really important.
4) do the stretches *a lot* even if it hurts (which it will if you're doign it right but talk to physio about how much hurt to settle for). If you've ever used a foam roller then it's going to be like that for a while when you do anything that pulls on the scar tissue and you'll find that the whole leg will begin to atrophy quite quickly when you're non-weight bearing.
5) once you're partial weight bearing walk a lot (I did 2-3 hours a day) - it really helps with building up strength and combined with stretches led to regaining full use.
I assume you'll get x-rays to make sure that bone necrosis hasn;t set in ont he ball of the hip due to loss of blood supply and hope this is all ok. I was told if I'd been 40 they'd have just gone straight to a replacement hip for this reason.
Also, talk to your surgeon and ask about having metalwork removed in the future - I had my bolts out after 2 years and if nothign else not trapping muscles between bolt heads and desk/table edges was worth an overnight stay in hospital and a couple of weeks off the bike.
sorry for the essay and hope your recovery goes well!