The thing that matters is the power imbalance, which would be nearly always present. This is highly undesirable, as it invalidates consent to a large degree (i.e. while the initial consent might be unquestionable, it gets really murky when things get into withdrawing it). It's similar as with employee-boss relationships and teacher-student. All of those can imaginably be okay, but the amount of dominance that the superior has over their partner makes things at least suspicious.
In fact, the "temperament" thing is one of the most commonly invalid, as having the "temperament" higher at 16 than 25 is not really that uncommon, intellect basically stays the same until 30, just gaining experience (!). And yet your 16 year old is (most likely) going to be dependent on their parents, and people will treat the older partner significantly more seriously even if they're a drunken slob, because the younger one is "a child" (and despite the older one being perceived as creepy. Ain't society great?).
In fact, the "temperament" thing is one of the most commonly invalid, as having the "temperament" higher at 16 than 25 is not really that uncommon, intellect basically stays the same until 30, just gaining experience (!). And yet your 16 year old is (most likely) going to be dependent on their parents, and people will treat the older partner significantly more seriously even if they're a drunken slob, because the younger one is "a child" (and despite the older one being perceived as creepy. Ain't society great?).