i think anyone can use it, in fact those who aren't active will of course see more drastic results. They'll be the ones most wiped out and sore-because the body's been lazy and out of shape for so long and is suddenly challenged.
The only caveat would be the usual "see your doctor first" idea before embarking on a program to try to ensure an out of shape system can handle it and see whether there are any propensities existing that could creat probs ie heart attack waiting to happen.
Then if you want a gentler, easier transition in to it, wade in slowly the first weeks. Do some jogging/walking, work running in to it until it's all running after weeks of it. Do some calisthenics, etc. - moderation at the beginning, accelerate the intensity, sets and reps over a period of time to mitigate the shock and health risks to someone out of shape.
Not only will it give someone the most athletic/muscular look, the program can be skewed towards greater size thru tweaks in the routines and increasing the resistance in calisthenics and weight/resistance band exercises.