Bruch and Newman (201

analyzed thousands of messages exchanged on a "popular, free online-dating service" between more than 186,000 straight men and women. They looked only at four metro areas—New York, Boston, Chicago, and Seattle—and only at messages from January 2014.
By analyzing patterns of messaging, they were able to establish the overall desirability of men and women in online dating based on their ages. They found that women's desirability was highest at the youngest age permitted on the dating site, i.e. 18 years old, and that it rapidly dropped as women aged. By contrast male desirability was relatively flat over time with a gentle peak by around age 50.
Observing the trend of desirability for women, it can be seen that the shape shows no signs of "leveling off" as it approaches 18. In a scenario where even younger women were allowed to participate, it seems likely the desirability would continue to rise by simple extrapolation of the existing curve trajectory.