I personally believe that weight gain as we age is normal. This doesn't mean that everyone will become overweight as an adult, but as you mature, so does your body. Our bodies continue to change throughout life...every part ages....it just is.
It's great that you are concious of your health and staying active now that you no longer do ballet. You're setting up good habits for yourself to follow as you age. However, you certainly don't need to worry about your weight at 5' 4" and 107 lbs., but to be aware of your health and maintain your level of fitness at any age is wise.
All the best!
"Weight loss is like driving: If you ever veer off the road, just make a u-turn and head back in the right direction.."
Highest Weight - 143 lbs (03/Sept/13)
Short Term Goal - 136.6 lbs (31/Oct/14)
Current Weight - 136.4 lbs (10/Oct/14) Back to a healthy BMI!
Goal Weight - 114 lbs (aiming for March 31, 2015!!)