How to stop feeling the anxiety of ageing? I'm only 31 right now?

Every day I feel like crap always seeing older men with much younger women and reading all the stuff about biology and how men prefer younger women.. I'm actually a bit scared to marry a guy my age or younger cause I fear he may leave me for a younger individual.. And I have crush on a older man but he is with a much younger woman...

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I don't want kids by the way..
How to stop feeling the anxiety of ageing? I'm only 31 right now?
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