I guess if we go by the actors ages, in Leon, Leon is 30, while Mathilda is 12. The gap is the same as between Wei Wei (34) and Ding Yi (16) but aged up.
I'd argue that in the movie, Leon hasn't mentally matured much past the age of 18, when he met significant trauma, while Matilda is mentally more mature for her age. (re: "I've stopped growing, I'm just getting older.") It feels like the director really wanted to make the audience uncomfortable though... Leon does come to realize that he loves Matilda, and gives everything that he has to her (tragically), whether it would have played out as a sexual (as Matilda wanted) or just continued as a fatherly relationship is left unknown.
How this related to Beloved, maybe it's in line with Wei Wei's feelings that she's been thrown into this situation, wants to help Ding Yi, but despite her adulthood, she doesn't have the proper experience or tools to help.