Formula Development: Age of Appearance

I am currently working on my next theory. But i need some help.

Often when at work the questions is posed "how old do I look".

I am proposed that anyone from 16-41 would like to be called between 21-28.

Are there different formulas for certain age ranges? or could there be one consistent formula? Different formulas exist for sexes I am sure.

I think a young man's preferred appearance age is between 25-28 while a woman's preferred age of appearance is between 21-25

I would love to hear your thoughts. I hope to have this posted sometime next week. Please comment with even the smallest ideas. Anything helps!