Clothes - wear it like you mean it. Charismatic people knows how to use their clothes to exude themselves. For an actor, you will wear the types of clothes that fit the character you are auditioning for. For a model, simplicity is key in making your whole appearance looks "flexible" enough for any type of clothes.
Sex - male or female, we're all equals. Men will usually be more daring in expressing their "charisma" (different levels) compared to females in general for the sole purpose that men is considered more proactive. But I believe both sexes can be equally charismatic.
Age - the older you get, the better. Like wine, good tastes come with age. Don't fret if you are young, for you have more energy and time is by your side. But older, more mature talents should be able to control themselves more and more patient in any situation.
Size & Posture - truly charismatic people are aware of their body language. Actors and models should be very aware of this, for every gesture may suggest certain nuances. Size matters too, for the taller and more toned you are, people in general looks up more to you. But the smaller and more petite form are still able to exert their charisma in other less obvious ways.
Speech - essential tool in communicating complex ideas. Used wisely can generate the intended results. Best keep it polite, short and to the point.
Non-verbal communication is the most unnoticed form of exuding your charisma. Simply sit in style or gesture someone politely to allude your charisma. Making others feel easy being around you is the point.
In conclusion, all the factors above are simply just an outward manifestation of the complex nature of charisma. Charisma is something that I believe you need to feel it within you truly before anything else. Even if you lack one or more of the factors mentioned above, you can still be charismatic in your own way, provided you know which is it.