Melissa -
My daughter is now 13 and has been taking dancing classes since she was 2; About 8 years ago, my wife (who also danced when she was a kid), signed up for an adult class that my daughter's teacher organized, just for exercise purposes. One of the older high school girls had to drop out due to a broken arm, and the teacher needed someone to fill in for the annual program, and she asked Linda, who signed on.
The next year, the same thing happened again. She had so much fun doing it the first two years that, the year after that, she just signed up to be in a class consisting of recent HS grads. She has danced every year since (except one year she had to drop out due to an illness), and she loves it. A few other adults have joined in from time to time, although she is typically the oldest. She looks great, too!
Linda says that it is great exercise. You might want to check the local kids dance schools to see if they have an adult program.