Answer:
Well, on paper, you must be at least 5 foot 8 and even then, in the modelling industry they call that short. If you're taller than that, you're much more likely to receive more bookings. Also, it depends on what type of modelling you want to do. For instance, in runway modelling they'd prefer you to be slim yet healthy, lean and extremely tall so that the variety of clothes they can pick and choose for you to model aren't as limited.