With guys, it’s generally more difficult to tell what age they are so long as they have no visible facial hair, wrinkles, or male-pattern baldness, whereas with gals, it’s only possible to fudge their ages so much in either direction: for any girl character below thirteen, your best bet is to cast a child actress roughly the same age, since it’s nearly impossible to disguise the curves girls start getting when pubescent, whereas boys don’t get any visible curves throughout adolescence unless they work on developing their muscles. Any actress over thirty, even if she’s well-preserved, is going to have a hard time playing a twenty-something character, let alone a teenager, while any well-preserved actor over fifty (with, as mentioned, no visible facial hair, wrinkles, or male-pattern baldness) can fairly easily continue to pass himself off as a suave and experienced thirty-year-old in a movie when partnered with a fresh-faced twenty-something actress like Grace Kelly.

Biology has also always supported a bit of a double standard socially: since a gal’s most fertile years run from about 16 to 26, those are typically considered the ages at which she is most attractive, whereas a guy’s fertility is fairly steady from pubescence onward, and his virility stands a good chance of lasting into old age (albeit almost inevitably with some decline even among the very well-preserved). Since gals traditionally are called upon to start bearing and raising the next generation as soon as possible, while guys are traditionally tasked with building a career and bringing home the bacon before they can go hunting for a bride, most societies consider it rather natural for somewhat older guys who are well-established financially to have a mutual attraction to younger gals in their prime childbearing years.

Then too, in the 1950s, most people associated tanning with youthfulness; whereas nowadays, you and I and most everyone else associate it with being crinkled up like a prune.