Nah, i think shes mentally 28 but i don't see how this is a strong argument aganst a posible ShinjixAsuka romance.
People are quite fond at this stage in the franchise about Kaworu and Shinji, and nobody even mentions Kaworu's age ? What about his mental maturity eh ? He seems pretty mature no ? Probably because the guy has acumulated knowledge for who knows how many milenia (if the looping is true).
The "she's older than him bla bla" has no weight at all and whoever brings it up has double standards.
A stronger argument against ShinjixAsuka is that Shinji never showed any interest in her, sexual or romantic.
So i think people should get over the "28 year old" argument.
Ultimately i don't think Anno gives a rats ass about the age difference between 2 chars, if he wants it to happen it will, but like i said, if he wanted a pairing that involved Shinji, he would have set the stage for one.
Well in 2.0 there was a stage, but it got nuked from orbit in 3.0 lol