I think there is much wisdom in the Church ordaining men only >25…however, I do not think it is technically impossible at all.
Some sources say Benedict XI became pope at only age 11 (I know his was not a sterling pontificate either) and Pope John XII (also with a bad record, so to speak, though he never taught error) died at the age of 27, having been made Pope at only 18. Of course in the Middle Ages the average life expectancy was only about 35 I think (of course skewed by the infant mortality rate).
Interesting topic though. I agree with the above poster that, as far as I know about the Sacrament of Holy Orders itself, there would be nothing to preclude someone having reached the age of reason from being ordained, technically speaking.