If a kind and generous Christian died 20 years ago, might their rebirth have resulted in there being a 19 year old person in the human realm now? If a kind and generous Christian died 20 years ago today, 21July2015, might their rebirth have resulted in there being a 19 year old person in the human realm now? I want to assume that the kindness and generosity perhaps trumped the ignorance about samsara, resulting in a new individual array of aggregates and store consciousness inclined toward learning about Buddhism and Nibana. I wonder this basis Theravada approach to rebirth.
I think it's difficult to talk about rebirth as if it were a sure thing: for example because kamma comes from a being's previous life, but it also comes from the life before that, etc.

"The [precise working out of the] results of kamma" is said to be unconjecturable.

Actually being able to directly see others' karmic destinations is one of the miraculous powers attributed to the Buddha:


  Then, the records tell us, in the first watch of the night he directed his concentrated mind to the recollection of his previous lives. Gradually there unfolded before his inner vision his experiences in many past births, even during many cosmic aeons; in the middle watch of the night he developed the "divine eye" by which he could see beings passing away and taking rebirth in accordance with their karma, their deeds; and in the last watch of the night he penetrated the deepest truths of existence, the most basic laws of reality, and thereby removed from his mind the subtlest veils of ignorance. When dawn broke, the figure sitting beneath the tree was no longer a Bodhisatta, a seeker of enlightenment, but a Buddha, a Perfectly Enlightened One, one who had attained the Deathless in this very life itself.