requirements
The fashion industry is rather fussy about who will represent its product. As such, your body must fit into industry-imposed standards.
As opposed to the women, male models usually start out between the ages of 18 and 25. Nobody's looking for a baby face because male buyers are usually older than females. Also, unlike most women, you'll be able to get work well into your 30s.
The average height for male models is between 5'11" and 6'2". As per your weight, it must be within the range of 140 to 165 pounds. The industry isn't looking for bulging muscles, but you definitely have to be fit.
If you have a lot of acne or acne scars, think about another career. You also need to be confident, responsible and organized to handle the pressure of being periodically rejected and working on a tight schedule. You must also be willing to relocate and travel to foreign cities.
breaking into the business
The stories you hear about models are always the ones that resemble a fairy tale. This guy was waiting in line to see a movie when a talent scout spotted him and signed him up to his agency. Unfortunately, this is the exception.
The way models get work is through an agent who gets a 10% to 33% cut. Some models can freelance, but that's not how they'll land the major gigs.
An agent will get you bookings, as well as advise you on how your career should develop. Here are the most common ways to get signed with an agency.
Source: http://www.askmen.com/money/how_to_200/217_how_to.html