Interesting question Auntbeez,
I can say that I wouldn't want either of the choices as there are several inherent problems with both. While a 20 year old body sounds good, it assumes that the 20 year old body is healthy and in shape. The mind of a 90 year old might quite likely have some level of dementia. It also assumes that a person learns many lessons as they age, thus becoming wise from experience. This is not necessarily the case for all individuals. Some go on to repeat the same mistakes over and over, never learning the lesson.
What frag will you be looking for tomorrow at the Frag Swap, and why?