From when I was working in one of the joints...
The less intelligent ones generally don't last all that long... They blow every time they take in, get bad habits, and get lazy and fat... They start believing their own PR... May blow bucks on a boob job or a nose job, but that's about it... Burnout by 22-23, either hooking or working low end jobs and going home to Bubba in the trailer park.
College girls exist, and they generally look at it as a part-time gig... Some will travel (cheap airfare or carpool) to an adjacent city where the odds of running into someone they know is lower. 16-20 hours on a weekend can pay some major bucks...
The smarter professionals can be downright predatory. Workouts and plastic surgery, anything to keep the ball rolling - they tend to sock it away too... Bit of circuit travelling - the "new girls" tend to do a little better sometimes... Downside of that is that they don't get the regular customers.
Sometimes the day gig is school, and sometimes the day gig is the health club... Remember one girl who went from going to the Y to a more upscale workout facility, with the prime intention of landing herself a trophy hunting husband... She quit working at the club about a month later.