Alchemy - Isaac of York

[NothaShrubry]

This is just an interesting question about the setting (1200ish) of Ivanhoe. I was wondering how old is the "old Jew" Isaac of York supposed to be. In the scene in the dungeons he is described as quivering and resisiting futiley, but Rebecca is still young - so what age is considered old in these times?

I also found interesting the overlap with alchemy. I haven't read a full copy of the entire text, but if anybody has read it, what do they know about the comtemporary understandings of alchemy. Is it mention used as a bluff, or in sincerity?