What is the key to longevity as a model. I know most industry professionals will tell you that a model's career isn't long and that you gotta enjoy while you got it, but there are models with staying power. What is the key to that?

As a photographer, I'm not against working with older models. What I look for:

1. Have they kept their physique? I haven't, much to my chagrin, but I'm behind the camera .

2. Have they not sun-damaged their skin? Tanning is evil to your skin. Smoking is evil to your skin. Protect your skin, moisturize, etc.

3. Have they kept their look updated? If a "model" in her 30's still has the "perm-n-poof" that was popular when we were both in high school, she's not getting any work from me. I don't expect a 30-something model to shop at Hollisters (though I still do at 30, and celebrate when I find something in my size), but up-to-date wardrobe is important.

4. For female models, have they kept their makeup style up to date? There's a reason why so many older actresses (the whole cast of Desparate Housewives, for example) look younger than they did a decade ago, and it's not all Botox.

My younger brother has been modeling for 20 years.  He started after college and has maintained a six-figure income from modeling for most of that time period. Basically, if you keep in shape and can be a decent visual representative of some marketable segment of the population, then you can model for quite a while.  It seems that men can model longer than women can in general, but I don't know if that is so true anymore since the median population is getting older.  It really depends a lot on the market an type of modeling work too.