Other than the age difference, what is wrong with her? Is she a mean person? Two_faced? Is she stupid? Lazy? Treat him like he’s a sugar daddy whose only goal is to spoil her? Does she behave like a 16 year old that’s going to grow up to be an awful adult? You didn’t really give any reason for being against this relationship and for thinking less of him other than the age difference, which I’m not sure is a valid reason to think less of either of them if they are happy together.
Why is “unproductive” in quotes?