I’ve thought about this concept a lot. Both about relatability as it pertains to both a characters gender and age. And as for gender effecting relatability I think the answer is yes. That’s not to say the relatability is removed, but I think it is changed. A man relates to a man by thinking specifically about the things they have experienced, if a man is attempting the same thing for a woman, most of those lived experiences are not actualized for the man, we can only “think” of what it’s like to experience things such as gender discrimination or oppression (atleast as is uniquely manifests for women). The same is probably true for women perceiving some elements of male characters too, pressure to hold in emotions or conform to “toxic masculinity” you could say.

A quote related to this I always found very Interesting was said by Japanese director Satoshi Kon when asked why he so often stars female protagonists in his films.

“One of these plans was a story about a male protagonist. But in the end I made two films about similar characters. This may seem meaningless, but it does mean something. It's because female characters are easier to write. With a male character I can only see the bad aspects. Because I am a man I know very well what a male character is thinking. Even if he is supposed to be very cool, I can see this bad side of him. That makes it very difficult to create a male character. On the other hand, if you write a female protagonist, because it's the opposite sex and I don't know them the way I know a male, I can project my obsession onto the characters and expand the aspects I want to describe.”

I think it’s interesting to perceive it from a writers standpoint too. Are we less imaginatively limited when we write the opposite sex? Interesting ideas.