If there should be Gaidal Cain in the story he would be born after the battle at Falme but before Birgitte was rapped out to WOT land. I find it difficult to believe that there were two Gaidals at the same time. That excludes Uno completely. Still that means new incarnation of Gaidal could not be more that about 2 years old. RJ could not allow himself to bring about 2 year old child since there's no fun in it. Other consideration is that it will be no fun if Gaidal does not fight in the Last Battle. Therefore, whoever the new incarnation of Gaidal is he has to come through two periods of rapid aging. As we know there are several places where rapid aging might occur. These are Tel'aran'rhiod, vacuole and possibly Finnland (interesting suggestion by Windy).

I would like to repeat that those two periods of aging should occur to anybody with the ambition to be Gaidal Cain. Obviously RJ may come with somebody else but one cannot build a theory on that suggestion. Olver is very much likely candidate (ugly, for example).

I cannot guess who did it to the boy but he was already imprisoned in some unpleasant place once and will be there for the second time. Probably he is on the way to it right now. Probably years of the life would be a price he will have to pay in the Finnland (quite a reasonable exchange), but that is a wild guess.

So my suggestion is rapid growing up (twice) for Olver. Last comment, I do not like the urchin, there's something about him that smells bad.