And the thing with trunks x mai aside from the obvious glaring issues of the age gap, it's just...so boring. Blah. Empty. Forced. No substance, no chemistry, nothing that stands out , no narrative parallels NOTHING.
When you look at other dragon ball ships, whether they're well written or make sense or not (let's be real this is dragon ball, none of the pairings are all that well written) they at least have something going for them. Be it fun banter or just having buzz or spark, something that makes it iconic. Bulma x Vegeta or Gohan x Videl are arguably 2 of the most popular ships in DB, why because they have something going for them. Gohan and Videl had a good dynamic that eventually blossomed into love and decent chemistry, Bulma and Vegeta are both firey and arrogant and play off each other so well. They're fun together!
Trunks x mai...is a huge nothingburger. They have no chemistry, no profound moments, there's no interesting banter or a good, compelling dynamic, they don't play off each other well, their personalities don't mesh well enough to make a good ship. It's very much gives "go girl, give us nothing!" Mai is not the kind of girl I would have imagined for Trunks, who would be an interesting match for him; not only was her entire character rewritten to attempt to make the ship work, but she's so unfathomably bland and uninteresting as a character herself. She lacks depth, she doesn't have the loud charisma of Bulma, or the passion of Videl (that she used to have before Super turned her into a Housewife (tm) she's just...generic female love interest with a gun. Who doesn't have any interesting traits or attributes to her. She's very much there to be forced in a relationship with someone much younger than her. And not only that but Trunks as a character had to be dumbed down and made stupid (I'm referencing present trunks mostly future trunks as a whole in super is a whole other issue in itself) to prop Mai up.
There's just nothing to like about it. It sacrificed both characters for it to be a thing, and that's the worse thing to do for a ship