You do not want to remind a woman that she is no longer young, and you do not want to remind a man that he is not old enough.
Call a man "boy" and he will take offence. Call a woman "old" and she will do the same. Why? Because both reminders touches at what each sex naturally values.
A man is offended by being called a boy because boyhood in his memory is the age of incompetence, foolish decisions, unrealised ambitions, and a lack of standing in the world. To call him boy is to dispute his progress. It suggests that he has not yet become the man he believes himself to be.
On the other hand, A woman is offended by being reminded that she is no longer young because youth is the period in which she enjoyed her greatest social advantage. Youth, for the average woman, is the season of beauty, attention, admiration, abundance of options, you name it. To remind her that she's no longer young is to remind her that it is passing is, that those privileges are passing with it.
Point is, The man wishes to distance himself from his younger self because it symbolises inadequacy. The woman wishes to remain attached to her younger self because it symbolises abundance.
This is why men are eager to prove they are older than they look, while women are eager to prove they are younger than they are.
The insult to the man is that he has not become enough. One to the woman is that she's no longer what she once was. Young and full of options.
The man measures himself by progress. He wants to hear, "look how far you've come".
The woman measures herself by preservation. She wants to hear, "You haven't changed at all."
The big message in this for you, the man is, when you remind a woman that she's no longer young, you remind her of her sexual market value. And now I believe I have said enough.