It's very simple really.. Provding you have the time, funds, health, age and a steady diet on your side it comes down to this:
The shape you have in the first place and how you respond to the drugs.
If you got a moderate shape and respond well you have a chance, If you have a good shape and respond moderatly you have a chance also.. If you have both then you have the best chance.
Shape = height, bone structure, muscle shape, joint size etc
Drug response = the amount it takes to enlarge what you got and how well you tolerate its effects/sides