Alejandro doesn't yet realize what he'd be putting the MC through. She's not likely to be accepted.
Regarding the age thing, he now looks her age, so I find that skeptical. She is only 16/17. That's not a huge age difference, though, if they were adults. Plus, Lorenzo looks like he's suffering from punishment from the jealous & possessive Alejandro. =P
Then there's also the super hot sensei (SHS)! :3
At this point it's either a love square or a love pentagon (note that an approved romantic rival will probably show up soon, and that presumes that the Emperor doesn't find out & try to hook the MC up with his son or that the son tries to take the MC for jealousy reasons, or the princess doesn't suddenly fall for Alejandro, or that the prince doesn't get sick from the curse). =P