I try to structure functions and validations like this in a early-return list at the top of a function.

    if(val <= someconstant)
        return; //not valid

    if(!(condition2 || condition3))
        return; //not allowed

    ...

I find it particularly useful in controller API functions because it makes the code a lot more auditable (any time I see the same set of conditions repeating a lot, I consider whether they are a good candidate for middleware).

I try to explain this to newer developers and they just don't get it, or give me eyerolls.

Maybe sending them this article will help.