I have to correct my earlier report, after some more testing and using the mod on an older savegame I get some weird results:
As seen in the pictures child characters can sometimes change to an adult portrait, and others to the generic portrait of a captain (those only availble to Yuan Shao). Also the new portrait seems to reflect the actual properties of the character meaning those with adult portraits can be used as generals despite being only one year old.
The oldest character I've seen with this was 17 years old, and once he became 18 he received a regular portrait. So the main problem is that characters become recruitable from the age of 1 instead of 18.
It would be interesting to know if this only affects savegames started without the mod though.
Edit: The bug seems to be there for new games as well. For an easy replication just start a Sun Jian campaign and wait one turn, you'll be able to recruit a 14-year-old Sun Ce.
Edit 2: The issues were caused by another mod which I obviously didn't suspect since it said it would only increase the chance of having children when it actually also tampered with the age of adulthood. Please excuse the inconvenience, mod is working absolutely fine & thanks for your work Dresden!